Population-based outcomes after 28,246 in-hospital vasectomies and 1,902 vasovasostomies in Western Australia.

OBJECTIVES: To examine trends in vasectomy and vasovasostomy, and the surgical complications and factors associated with reversal after vasectomy, and paternity after vasovasostomy. PATIENTS AND METHODS: Procedure rates were estimated from 1980 to 1996 in the population of Western Australia. Linked hospital morbidity records were used in the follow-up of men after vasectomy to estimate the risks of complications and reversals. Records of vasovasostomies were linked to the paternity field on birth registrations. Independent effects of the study factors were examined using Cox regression. RESULTS: There was little net change in vasectomy rates, whereas vasovasostomy rates increased in men aged 30-49 years. Risks of surgical complications were low and decreased for vasovasostomy. At 12-15 years after vasectomy, the risk of reversal levelled at 2. 4% in the total cohort and at 11.1% in men aged 20-24 years. The risk of vasovasostomy was 69% greater after vasectomy performed in 1994-96 than in 1980-84 (P = 0.011). The factors strongly associated with reversal were age < 30 years and being single, divorced or separated at the time of vasectomy. Paternity was achieved after an estimated 53% of vasovasostomies. Successful reversal was more likely if the man was younger at vasectomy and the time elapsed was comparatively short. Compared with vasovasostomies performed in 1980-84, the success rate of those in 1994-96 was almost four times higher. CONCLUSION: Population rates of vasectomy are stable but the risk of seeking a reversal has increased. Outcomes after vasovasostomy have improved. Care should be taken during the counselling of men before vasectomy, and especially in those aged <30 years.

Population-based linkage of health records in Western Australia: development of a health services research linked database.

OBJECTIVES: To introduce the Western Australian Health Services Research Linked Database as infrastructure to support aetiologic, utilisation and outcomes research. To compare the study population, data resources, technical systems and organisational supports with international best practice in record linkage and health research. METHOD AND RESULTS: The WA Linked Database systematically links the available administrative health data within an Australian State of 1.7 million people. It brings together, initially, six core data elements (birth records, midwives' notifications, cancer registrations, in-patient hospital morbidity, in-patient and public out-patient mental health services data and death records). It will be updated regularly and is designed, in future extensions, to include data on primary, residential and domiciliary care and health surveys. Linkage uses probabilistic matching of patient names and other identifiers. Geocodes for spatial analysis are assigned using address linkage and mapping software. By June 1997, the project had taken 2 1/2 years to develop the system and link seven million core data records from 1980 to 1995. CONCLUSIONS: The system is consistent with international benchmarks, from four centres of excellence, for the study population, core datasets, matching and geocoding, and collaborative networks. There are prospects to redress deficiencies in primary medical contact and other data resources, validation studies, tracing systems and a more supportive legal framework. IMPLICATIONS: The WA Linked Database will be used in combination with medical record audits to provide a comprehensive evaluation of health system performance.

Validation of linked administrative data on end-stage renal failure: application of record linkage to a 'clinical base population'.

OBJECTIVE: To evaluate the use of record linkage to monitor the occurrence of end-stage renal failure in Western Australia in 1980-94. METHODS: A clinical base population of 1,046 patients was identified from the Western Australian (WA) Health Services Research Linked Database. To exclude acute renal failure, patients were selected if they received in-hospital renal dialysis on more than 10 occasions over more than 28 days in 1980-94. Estimates of annual incident and prevalent cases were validated against the ANZDATA dialysis and transplant register. Reasons for discrepancy were investigated by an ad hoc linkage between the two data sources. RESULTS: The WA Linked Database counted slightly fewer incident cases (-7%) and slightly more prevalent cases (+7%) than the ANZDATA Register. The Linked Database identified 97% of cases on the ANZDATA Register, but this fell to 83% post case definition, probably due to patients receiving home-based dialysis failing to meet our case definition. ANZDATA correctly identified 90% of cases in the linked file. CONCLUSION: Trends in end-stage renal failure from 1986 to 1994, based on the Linked Database, were the same as those reported from purpose-designed disease registers. IMPLICATIONS: Linked administrative data provide a valid and efficient means to plan and evaluate many of the routine aspects of renal dialysis and transplant services.

Trends in repeat prostatectomy after surgery for benign prostate disease: application of record linkage to healthcare outcomes.

OBJECTIVE: To compare the risk of repeat prostatectomy for benign prostatic hyperplasia (BPH) in a population-based cohort of 19 598 men in Western Australia treated by transurethral resection of the prostate (TURP) or open prostatectomy over a 16-year period. PATIENTS AND METHODS: The Western Australian Health Services Research Linked Database was used to extract all hospital morbidity data, death records and prostate cancer registrations for men who had prostate surgery for BPH in 1980-95. The cumulative incidence of first repeat prostatectomy calculated using the actuarial life-table and incidence-rate ratios of the first repeat prostatectomy, comparing TURP and open prostatectomy, were obtained using Cox regression. RESULTS: The cases comprised 18 464 TURPs and 1134 open prostatectomies, from which there were 1095 subsequent repeat prostatectomies. After adjustment for calendar time, age and admission type, the incidence rate of the first repeat prostatectomy was up to 2.30 times higher (95% confidence interval, 1.62-3.27) after initial TURP than for initial open prostatectomy. The absolute risks at 8 years for TURP was 6.6%, and was 3.3% for open prostatectomy. CONCLUSION: The absolute risk of a repeat prostatectomy for TURP and open prostatectomy were consistent with the best reported international experience. There was evidence that the risk in 1990-95 had declined compared with earlier periods, despite a shift towards more closed procedures. The differential risks of repeat prostatectomy should be explained to patients and considered in the development of clinical guidelines, notwithstanding the advantages of TURP over open prostatectomy in terms of surgical morbidity and cost.

Mortality and prostate cancer risk in 19,598 men after surgery for benign prostatic hyperplasia.

OBJECTIVES: To examine postoperative mortality and prostate cancer risk after the first prostatectomy for benign prostatic hypertrophy over a 17-year period in a population-based cohort of men in Western Australia, using improved methods to adjust for comorbidity. PATIENTS AND METHODS: The relative survival from death and prostate cancer incidence was calculated against the background population rates. The outcomes of transurethral resection of the prostate (TURP) and open prostatectomy (OP) were compared adjusting for calendar year, age, admission type and comorbidity using Cox regression. Fractional polynomials were used to take account of nonlinearity in confounder effects. RESULTS: At 10 years, the relative survival was 116.5% in TURP patients and 123.5% after OP. Adjusting only for confounding by age, calendar year and admission type, TURP had a higher mortality rate than OP (rate ratio, RR, 1. 20; 95% confidence interval 1.08-1.34). The RR fell to 1.10 (0.99-1. 23) after adjustment for comorbidity and to 1.07 (0.95-1.19) when accounting for nonlinearity. The relative survival from the incidence of prostate cancer at 10 years was 103.7% after TURP and 104.5% after OP. The RR adjusted for age and calendar year was 1.44 (0.94-2.21) for incidence and 1.37 (0.81-2.29) for prostate cancer mortality. CONCLUSION: There is at most a small and clinically unimportant excess mortality risk from TURP; any difference could be due to a protective effect of OP on the long-term risk of prostate cancer and a lower rate of repeat prostatectomy.

Prostate cancer in Western Australia: trends in incidence and mortality from 1985 to 1996.

OBJECTIVE: To measure trends in recorded incidence and mortality rates of prostate cancer in Western Australia from 1985 to 1996 and to relate these to prostate-specific antigen (PSA) testing for prostate cancer. DESIGN: Descriptive study based on data from the Western Australian Cancer Registry, the Australian Bureau of Statistics and the Health Insurance Commission. DATA: All newly diagnosed cases of prostate cancer and all deaths from prostate cancer in Western Australia from 1985 to 1996. MAIN OUTCOME MEASURES: Recorded incidences and mortality rates for prostate cancer. RESULTS: After increasing steadily from 42 per 100,000 person-years in 1985 to 61 in 1992, the recorded incidence more than doubled to 134 per 100,000 person-years in 1994, then fell sharply to 87 in 1996. Among men aged 50 years or more, those aged 50-54 years had the largest annual increases: 14% (95% confidence interval [CI], 10%-19%) from 1985 to 1992 and 108% (95% CI, 84%-134%) from 1992 to 1994. They also had the smallest annual decline between 1994 and 1996 (8%; 95% CI, 1% increase to 16% decrease). The mortality rate showed no sudden increases or decreases. In men aged 60 years or older, the mortality rate increased annually by 2.9% (95% CI, 2%-4%) from 1985 to 1996. The number of Medicare reimbursements for PSA tests increased until May 1995, then fell. There was a significant correlation between the monthly number of PSA tests and new cases of prostate cancer (P < 0.01). CONCLUSIONS: Following a period of steady increase, the recorded incidence of prostate cancer increased dramatically in 1992 because of screening by PSA testing. From 1994, these incidence figures declined almost as sharply, partly because of reductions in testing. The mortality rate has not shown any systematic deviation from its long-term trend.

The Quality of Surgical Care Project: a model to evaluate surgical outcomes in Western Australia using population-based record linkage.

BACKGROUND: The aim of this study is to establish a model to evaluate surgical outcomes and, where indicated, recommend changes to improve the quality of surgical care in Western Australia (WA). Open resection for aneurysm of the abdominal aorta was the first procedure evaluated and the results are reported in an accompanying paper. METHODS: The Quality of Surgical Care Project (QSCP) is conducted under the aegis of the Royal Australasian College of Surgeons (RACS) in WA, and brings together a multidisciplinary team of surgeons, public health researchers and health service administrators. The Western Australia Health Services Research Linked Database (the WA Linked Database) is used to provide linked chains of patients records residing in the state health department from the following sources: hospital morbidity data system, birth and death records, mental health services data, cancer registrations and midwives' notifications. This links 16 years of population-based patient records from 1980, including all public and private hospital admissions and re-admissions. The Quality of Surgical Care Project was established to use and to correlate the data from the WA Linked Database. RESULTS: The result is a powerful database for a contained population that is available for scientific analysis by a multidisciplinary team of clinical epidemiologists, surgeons and health service managers. Users will have the ability to establish benchmark standards for the outcomes of surgical procedures in WA for use in quality improvement programmes run by the College and will facilitate self-directed performance auditing activities as a commitment to greater community accountability. CONCLUSIONS: The Quality of Surgical Care Project provides a potential model of benefits to be realized by both the medical profession and the community through multidisciplinary collaboration supported by adequate information. Although migration from WA is relatively low, future linkage to the state electoral roll will allow correction for any population change.

Hospitalisation of the elderly during the last year of life: an application of record linkage in Western Australia 1985-1994.

STUDY OBJECTIVE: To measure the trend, pattern, and cost of time spent in hospital during the last year of life in Western Australia and to identify trends in the place of death. The results were compared with those reported from the Oxford Record Linkage Study. DESIGN: Mortality records for those aged 65 years and over were linked to inpatient hospital morbidity records with a date of separation within one year before death. Comparative inpatient resource utilisation was estimated using ANDRG 3.0 cost weights for Australian public hospitals. SETTING: Western Australia. PARTICIPANTS: All 68,875 persons aged 65 years and over who died between 1 January 1985 and 31 December 1994. MAIN RESULTS: Increasing proportions of all age groups (65-74, 75-84, and 85+ years) were admitted to hospital at least once in the year before death during 1985-94, but the chance of admission decreased with age. There was a trend towards a greater number of shorter admissions per person. Total bed days per person showed no significant increase, except at ages 65-74 years. Total inpatient resource utilisation during the last year of life was lowest and remained constant in those aged 85 years and over, while increasing gradually (3.7% per annum) in the younger elderly. The Western Australian population spent more time in hospital in the last year of life at ages 65-74 years, but the advanced elderly spent less time in hospital, when compared with the Oxford Region. CONCLUSIONS: Recent gains in life expectancy and higher per capita health expenditure have not been accompanied by more time spent in hospital during the last year of life at ages 75+ years. International differences between Western Australia and Oxford can be explained by differences in aged care provision.

Viral meningitis due to echovirus types 6 and 9: epidemiological data from Western Australia.

During the autumn of 1992, Western Australia experienced a large viral meningitis outbreak of dual aetiology. Of the 161 cases, 64% were children under 15 years of age, with the highest notification rate being in children less than 5 years of age. Echovirus 9 caused 41% of cases and occurred mainly in the metropolitan areas of Western Australia whereas echovirus 6, which caused 37% of cases, was more widespread. An enterovirus was cultured from 70% of CSF specimens, 88% of faecal specimens and 68% of upper respiratory tract specimens. High CSF white cell counts and neutrophil predominance were common. Seven cases had normal CSF white cell counts even though an enterovirus was isolated from the CSF. Therefore, the CSF findings were of restricted value in excluding viral meningitis, and did not reliably distinguish between bacterial and viral meningitis.

Changing epidemiology of methicillin-resistant Staphylococcus aureus in Western Australia.

OBJECTIVE: To assess the epidemiology of methicillin-resistant Staphylococcus aureus (MRSA) in Western Australia. DESIGN: Retrospective review of statutory notification data. SETTING: Western Australia (WA), 1993. OUTCOME MEASURES: Notification rates, antibiotic resistance patterns and classification of isolates as imported or WA MRSA strains on the basis of antibiotic susceptibility. RESULTS: There were 204 notifications of MRSA, 78% of which were classified as WA MRSA. Three outbreaks of MRSA infection and colonisation occurred in separate WA hospitals. Notification rates per 100,000 were highest in the rural regions: the Kimberley (86.32), Goldfields (62.47), Mid West (37.21) and Pilbara (27.38) regions; and lowest in the metropolitan regions (5.52). All MRSA isolates were susceptible to vancomycin. Most imported strains were susceptible to amikacin, bacitracin, chloramphenicol, framycetin, fusidic acid and novobiocin, but only 23% to gentamicin. WA MRSA strains remained predominantly susceptible to all antibiotics tested, except beta-lactams, erythromycin and tetracycline, but a few strains resistant to rifampicin (1%) and fusidic acid (3%) appeared in the second half of 1993. CONCLUSIONS: The epidemiology of MRSA in WA is changing rapidly, with increases in both the numbers of notifications and the proportion from country regions. A new strain of MRSA (WA MRSA) that is less resistant to antibiotics than imported MRSA has emerged and is threatening the State's success in preventing establishment of MRSA in its hospitals.

Methicillin-resistant Staphylococcus aureus in Western Australia, 1983-1992.

A statewide screening programme has prevented imported strains of methicillin-resistant Staphylococcus aureus (MRSA) from becoming established in any hospital in Western Australia (WA). Recently, notifications of MRSA in WA have increased, prompting a review of surveillance data for the period 1983-1992. Our aims were to determine: (i) the distribution by age and sex of persons with MRSA; (ii) changes in notification rates over time and by location in WA; and (iii) temporal changes in antimicrobial resistance patterns. There were 631 notifications of MRSA for the 10 year period 1983-1992, ranging from a low of 36 in 1988 to a high of 117 in 1992. When the distribution by age and sex was examined, three age group peaks were apparent: 0-9 years, 20-39 years and 60-79 years. There was a predominance of females in the 20-39 years age group, reflecting a greater proportion of hospital nursing staff carrying MRSA. In those aged 50 years or more, there was a marked predominance of males. The highest notification rates overall occurred in the remote Kimberley region of WA, however, rates increased significantly in all regions of the state in 1992. Based on antimicrobial resistance patterns, MRSA was classified into two groups: multiresistant imported strains which often caused outbreaks in hospitals; and a less resistant MRSA (WA MRSA). WA MRSA appears to have originated in the Kimberley region and then spread widely in the community to other regions of the state, and the proportion of WA MRSA has increased significantly since 1989.

Acute symptoms and sequelae of Ross River virus infection in South-Western Australia: a follow-up study.

BACKGROUND: Unusually high tides along the south-west coast of Western Australia (WA) during the spring and summer of 1988-89 provided ideal breeding conditions for mosquito vectors of Ross River virus (RRV). This was followed by the biggest outbreak of RRV infection ever documented in WA (330 notified cases). OBJECTIVES: To describe the nature and duration of symptoms of RRV infection in WA, and associated functional disability; to determine the perceived effectiveness of treatments; to determine the usefulness of available information on RRV infection. STUDY DESIGN: A retrospective study of all cases of RRV infection reported from South West WA during the 1988-89 outbreak, using a self-administered patient questionnaire. RESULTS: The most common symptoms were arthralgia, tiredness and lethargy, and joint stiffness and swelling. In patients with joint manifestations, the knees, wrists and ankles were almost always affected. Non-steroidal anti-inflammatory agents, rest, simple analgesics and hydrotherapy were subjectively the most helpful treatments. Only 27% of patients had recovered completely within 6 months of onset of symptoms. Three years after the outbreak, up to 57% still experienced at least intermittent joint symptoms. Less than one-third of people reported that the available information adequately explained the consequences of RRV infection. CONCLUSIONS: Compared with patients elsewhere in Australia, people infected with RRV in the South West of WA experience a slightly different spectrum of clinical symptoms, with a longer period of disability. This may be related to the presence of a different topotype of the virus to that found elsewhere in Australia. Better information for doctors and patients on the likely course of the illness is needed. Future studies should examine the economic cost associated with RRV infection, and evaluate treatments to shorten the period of disability.

Biochemical and neurohormonal responses to the introduction of a lacto-ovovegetarian diet.

OBJECTIVE: To assess the mechanisms of the blood pressure-lowering effect of a vegetarian diet in the early and later stages of dietary intervention. DESIGN: After 2 weeks without intervention (baseline), 20 normotensive men were matched for age and body mass index and randomly allocated to an omnivorous (control) or a lacto-ovovegetarian diet for 6 weeks in a parallel trial. METHODS: Ambulatory blood pressures were recorded between 0800 and 1700 h on alternate days during the first week of intervention, twice in the second week and weekly thereafter. Blood samples collected after a standard breakfast were analysed for plasma noradrenaline, adrenaline, atrial natriuretic peptide (ANP), renin, aldosterone, glucose and insulin. Factor and multiple regression analyses were used to assess the association among neurohormonal factors, blood pressures and diet. Results were analysed for the first week of the diet and for the entire 6 weeks. RESULTS: Ambulatory blood pressures at work were lower on the vegetarian diet than in the controls. This blood pressure decrease was associated with a factor representing lower plasma catecholamine and renin activity levels throughout the study, and a factor representing reduced plasma glucose and insulin levels in week 1 of intervention only. Plasma ANP levels were significantly higher during week 1 of the vegetarian diet. CONCLUSIONS: A blood pressure lowering effect of a vegetarian diet during normal working activity was shown. Using factors derived from the biochemical variables, results were in keeping with the hypothesis that these effects may be mediated by reduced sympatho-adrenal activity consequent to altered glucose and insulin handling. An early increase in plasma ANP may contribute to the blood pressure reduction.

Respiratory disease in non-smoking Western Australian goldminers.

Respiratory symptoms, spirometry, and transfer factor were measured in 208 non-smoking Western Australian underground goldminers (mean age 32) to identify the presence of respiratory abnormalities resulting from underground work. These subjects were part of a larger group of 771 subjects attending for statutory periodic chest x ray examinations in the industry. They had worked underground for a median of three years. The prevalence odds ratios of bronchitis, dyspnoea, wheeze, and asthma all tended to be related to duration of underground employment, even after adjusting for age, those for wheeze and asthma reaching statistical significance. After adjusting for age and height the duration of employment also had a significant effect on TL/VA but not on FEV1, FVC, or TL. These changes are consistent with the presence of airway narrowing and non-specific lung fibrosis or emphysema in non-smoking underground goldminers.

A factorial study of salt restriction and a low-fat/high-fibre diet in hypertensive subjects.

OBJECTIVE: To compare the independent and additive effects of sodium restriction and a low-fat, high polyunsaturated: saturated fatty acids (P:S) ratio, high-fibre diet upon blood pressure. DESIGN: A randomized, parallet, double-blind, placebo-controlled (for sodium) 2 x 2 factorial trial. SETTING: Clinical. PARTICIPANTS: Ninety-five hypertensive subjects (mean blood pressure, 137/83 mmHg), mean age 53.5 years, consuming less than 30 ml ethanol/day were selected from community volunteers. Seventy-nine treated and twelve untreated hypertensives completed the trial. INTERVENTION: Subjects followed either a low-sodium, low-fat/high-fibre diet (less than 60 mmol sodium/day; 30% fat energy; P:S ratio = 1; 30-50 g fibre/day) or a low-sodium, normal-fat/normal-fibre diet (less than 60 mmol sodium/day; 40% fat energy; P:S ratio = 0.3; 15 g fibre/day) for 8 weeks. Half of each group received 100 mmol/day NaCl and the remainder received placebo. MAIN OUTCOME MEASURES: Blood pressure and blood lipids. RESULTS: Sodium restriction significantly reduced standing and supine systolic blood pressure, with no effect upon diastolic blood pressure. The low-fat/high-fibre diet had no effect upon blood pressure, but significantly reduced total cholesterol, low-density lipoprotein cholesterol and high-density lipoprotein cholesterol. CONCLUSIONS: Sodium restriction reduced blood pressure and did not raise low-density lipoprotein cholesterol. A low-fat/high-fibre diet did not reduce blood pressure but lowered cholesterol levels. A combination of the two regimes has the greater potential for reducing cardiovascular risk in hypertensives.

An investigation of hypertension in a slum of Nakhon Ratchasima.

There is evidence that Thai people living in slums may be at high risk of developing hypertension. The present study was undertaken on a random sample of 1,000 subjects aged 20 and over living in a slum in Muang district of Nakhon Ratchasima during 1 February to 31 may 1988. This study consisted of measurements of blood pressure and body build, with administration of an interview on demographic characteristics, sociocultural factors and food frequency patterns. The results were based on 804 respondents. It was found that the prevalence of hypertension was 16.9%, nearly half of the hypertensives being mild cases. Only a low proportion of the proven cases was both aware of their condition and receiving treatment. About one fifth of the treated cases had blood pressure under 160 mm Hg systolic and 95 mm Hg diastolic. Based on these findings, it is concluded that these slum inhabitants are at high risk of developing hypertension. Community interventions are needed in order to prevent complications related to hypertension. Health education aimed at increasing community awareness of hypertension should be a major component of the community intervention.

Comparison of diets supplemented with fish oil or olive oil on plasma lipoproteins in insulin-dependent diabetics.

This study was designed to compare changes in high-density lipoprotein (HDL)- and low-density lipoprotein (LDL)-cholesterol in normolipidaemic male insulin-dependent diabetics (IDD) following dietary supplementation with either the fish oil concentrate Max EPA or olive oil. The contribution of the small quantity of cholesterol in Max EPA to these changes was also examined. Twenty-seven subjects were matched in groups of three and randomly allocated to one of three treatment groups of nine subjects each. Subjects were given 15 1-g capsules of oil daily for 3 weeks, consisting of either Max EPA, olive oil, or olive oil to which was added the same amount of cholesterol as contained in Max EPA, respectively. There was a significant increase in eicosapentaenoic acid, and a decrease in arachidonic acid, in the platelet membrane phospholipids of subjects taking Max EPA. In this group, there was an approximately 30% increase in serum HDL2-cholesterol (0.59 +/- 0.07 to 0.77 +/- 0.11 mmol/L, mean +/- SEM; P less than .01) and a corresponding decrease in HDL3-cholesterol (0.79 +/- 0.03 to 0.71 +/- 0.03 mmol/L; P less than .05). Although total and LDL-cholesterol concentrations were also higher after Max EPA, the changes were not significant. Triglycerides were significantly decreased by Max EPA. There were no significant changes in lipids in the groups given olive oil. These results show that compared with olive oil, dietary supplementation with Max EPA substantially increases HDL2-cholesterol in insulin-dependent diabetics. This is most likely due to a selective effect of omega 3 fatty acids.(ABSTRACT TRUNCATED AT 250 WORDS)

Measuring the HIV epidemic: the Western Australian experience.

Previous discussion about sources of error in measuring the human immunodeficiency virus (HIV) epidemic has tended to emphasise errors which underestimated the number of HIV infected persons. Data are provided from Western Australia illustrating potential errors which may result in overestimating the size of the epidemic. Duplication of persons notified in more than one State and multiple notifications by doctors and laboratories of single cases may give rise to substantial errors in over-estimation.

A factorial study of fat and fibre changes and sodium restriction on blood pressure of human hypertensive subjects.

1. Diets used to reduce sodium intake often involve changes in fats and fibre which might themselves affect blood pressure and/or lipid metabolism. To evaluate the relative importance of these dietary changes for the management of hypertension we have studied the independent and additive effects of sodium restriction (less than 60 mmol/day) and a low fat (30% energy), high P/S ratio (1.0), high fibre (30-50 g/day) 'cholesterol lowering' diet. 2. Ninety-five hypertensives entered a four group parallel study with a factorial design. Following 5 weeks familiarization subjects [BP range 109/66-168/105 mmHg] were randomly assigned to either a 'low sodium, cholesterol lowering' diet or a 'low sodium, cholesterol maintaining' diet. Half the subjects in each group were then assigned to 100 mmol/day NaCl supplement and the remainder to placebo. These diets were continued for 8 weeks. Seventy-nine of the 91 hypertensives who completed the study were on antihypertensive therapy throughout. 3. Mean urinary sodium excretion decreased from 137 (54 mmol/day (n = 43) at baseline (B) to 52 (32) mmol/day (n = 45, P = 0.0001) during intervention (I) in the low sodium groups and remained unchanged in the groups which received slow sodium (B = 129 [46], n = 43; I = 134 [29], n = 42). Diet record and plasma fatty acid analysis confirmed that the dietary aims of the study were achieved. 4. Sodium restriction reduced supine and standing systolic BP by a mean (+/- s.e.m.) of 6 +/- 2 and 6 +/- 4 mmHg, respectively (P less than 0.005).(ABSTRACT TRUNCATED AT 250 WORDS)