[Replacement of mycophenolate mofetil with azathioprine in patients with renal transplants]. / Zamena mikofenolat mofetila azatioprinom kod bolesnika sa presadjenim bubregom.

Numerous clinical studies demonstrated that mycophenolate mofetil (MMF) was significantly more effective in prevention of acute rejection episodes than azathioprine. Since the data supporting the long-term benefits of MMF therapy are not available, and considering the high cost of this therapy, we examined the safety of conversion from MMF to azathioprine in renal transplant patients. In 12 renal transplant patients (4 cadaveric and 8 living related donors) on triple immunosuppressive therapy (prednisone/MMF/cyclosporine) conversion from MMF to azathioprine was done after the first six to twelve post-transplant months. The majority of patients were in the low immunological risk of transplantation, and 7 (58.3%) received antithymocite globulin due to the delayed graft function. The mean follow-up period after the conversion to azathioprine was 6.4 months (range 3-12 months). Acute rejection episode was noticed only in one patient 8 months after the conversion following acute graft pyelonephritis. In all other patients graft function remained unchanged. We have concluded that the conversion from MMF to azathioprine in renal transplant patients on triple immunosuppressive therapy is safe and without detrimental effects on short-term allograft function. Long-term follow-up studies on larger number of patients are needed to confirm these observations.

Locally produced specific cytomegalovirus immunoglobulin for intramuscular use as a therapy in renal allograft recipients.

Immunomodulator, i.e. specific hyperimmune anticytomegalovirus immunoglobulin for intramuscular administration, produced in 1999 with the aim of prevention of CMVI, and the development of the disease, was for the first time applied in kidney transplant recipients in January 2000, in the Center for kidney transplantation at the Military Medical Academy. Therapy was administered in four cytomegalovirus (CMV)--seronegative kidney recipients from CMV-seropositive donors--the combination that in the majority of cases lead to the development of CMVI/disease resulting in transplant rejection. Patients received 0.2-0.3 ml/kg of cytomegalovirus immunoglobulin (CMVIG) 6 hours before the transplantation, and subsequently the same dose during the following 5 weeks. Simultaneously, they received ganciclovir in therapeutic doses adjusted according to creatine clearance during the first three post-transplantation months (2 weeks parenterally, the rest orally). Kidney transplant recipients tolerated well i.m. applied CMVIG without any adverse effects. Test result obtained from the Paul-Erlich Institute, Germany in 1999 spoke in favor of the quality of the first national CMVIG preparation.

[Use of mycophenolate mofetil in patients with a transplanted kidney and cyclosporin nephrotoxicity]. / Primena mikofenolat mofetila kod bolesnika sa presadjenim bubregom i ciklosporinskom nefrotoksicnoscu.

Cyclosporine (CsA) nephrotoxicity is an important problem in renal transplant recipients, which can influence long-term graft survival. The safety of conversion from CsA to azathioprine (AZA) remains controversial and can result in higher incidence of acute rejection. Mycophenolate mofetil (MMF) is a new immunosuppressive agent superior to AZA in the prevention of acute rejection. Five patients with cyclosporine nephrotoxicity were converted from CsA/AZA/prednisolon to MMF/prednisolon protocol. All patients had low immunological risk and 4 out of 5 patients received antithymocyte globulin before conversion as the induction therapy or as the treatment for acute rejection. Mean follow-up after conversion was 16.8 months (range 4-32 months). No patient experienced acute rejection during follow-up period. The mean serum creatinine concentration decreased from 219 +/- 44.18 (range 168-280) to 122.6 +/- 48.02 mumol/l (range 72-187 mumol/l) (p = 0.002). Arterial hypertension improved after CsA withdrawal in 20% of patients. We have concluded that, in selected patients with cyclosporine nephrotoxicity, CsA withdrawal with concomitant use of MMF is safe and effective in the improvement of graft function and arterial hypertension.

[Results of kidney transplantation at the Institute of Urology and Nephrology of the Serbian Clinical Center in Belgrade]. / Rezultati transplantacije bubrega u Institutu za urologiju i nefrologiju klinickog centra Srbije u Beogradu. Rezultati Rezultati Rezultati transplantacije bubrega u Institutu za urologiju i nefrologiju Klinickog centra Srbije u Beogradu.

UNLABELLED: Over the period 1980-1992 256 kidney transplantations were carried out in the Institute of Urology and Nephrology, Clinical Centre, Belgrade: 105 (41%) from cadaveric and 151 (59%) from alive related donors. The first kidney transplantation was performed in our Institution in 1974; however, in the first decade only 27 kidney transplantations were performed. Since 1987, thanks to an increasing number of living kidney donors, the number of transplantations continually increased, and after that period an average of 30 kidney transplantations are performed annually (Figure 1). The aim of the study was to establish the survival of patients and grafts, and factors influencing this survival, as well as to determine the causes of patients' death and graft loss. All the patients were followed-up in our outpatient department within at least 5 years to maximum 17 years. Drug combination therapies were changed in the observation period. From 1983 cyclosporin A (CyA) was added to azathioprine (Aza) and prednisolone (Pr). An increasing number of patients with high immunological risks necessitated the strongest initial immunosuppressive treatment with ALG in addition to Aza and Pr. CyA in a dose of 8 mg/kg b.w. was introduced when serum creatinine concentration fell below 300 mumol/L. The triple treatment including CyA, Aza and Pr was the most common maintenance immunosuppressive therapy in our patients. RESULTS: One and five years survived 95% and 75% of patients, and 84% and 52% of grafts. In assessing the impact of donor source, the year of transplantation, and age of donors we obtained the following results: Living related grafts survived better than cadaver grafts, especially during the first posttransplantation year (Figure 2). Furthermore, graft survival rates from 1987 to 1992 were significantly better than those from early period i.e. 1980 to 1986 (Figure 3). The significantly worse survival rate for grafts from donors older than 60 was noted than for grafts from younger donors. Searching for factors influencing the survival, non immunological and immunological differences between donors and recipients were analyzed. Our analysis showed that 50 living related donors were older than 60. In addition, the majority of them were 20 years older than their graft recipients. Two and more HLA mismatches were observed in 46% of our transplant patients, and 20 patients were highly sensitized. However, the immunological risks were higher in living related transplantations: different ABO blood groups, historical positive cross match reaction between donors and recipients (Table 1). A multivariate analysis using Cox proportional hazards model was performed to determine the important independent predictors of graft survival, and it revealed the following factors (Table 2): number of acute rejections, graft function at the end of the first month and until the end of the first posttransplant year, donors' age, and age and sex differences between donors and recipients. The occurrence of acute rejection at any time had a significant negative effect on graft survival. Since better HLA matching is likely to mean less early rejection it could be concluded that HLA matching influenced graft function and survival in our patients. Absence of acute rejection and delayed graft function or acute tubular necrosis were associated with an improvement of the graft function based on serum creatinine concentration, indicating that delayed graft function also influenced graft survival. The relative risk of graft loss was 2 times higher for patients receiving graft from donors older than 60. Until December 1997, when our analysis was done, of 256 kidney transplant patients 156 lost their grafts. The major causes of graft loss (Table 3) in the early period from 1980 to 1986 were non immunological such as acute tubular necrosis, vascular thrombosis and patients death with functioning graft. (ABSTRACT TRUNCATED)

[Analysis of a 4-year follow-up of the results of kidney transplantation from living related donors]. / Analiza cetvorogodiznjeg pracenja rezultata transplantacije bubrega od zivog srodnog davaoca.

The aim was to present a four-year experience in living related kidney transplantation. A total of 43 patients (9 females and 34 males) were enrolled in this study. The standard triple immunosuppressive therapy (steroids, azathioprine and cyclosporine) was administered in 19 (44.1%) patients, and in 20 (46.5%) mycophenolate mophetil in daily dose of 2 g instead of azathioprine. In 5 (14.2%) patients with high immunological risk and delayed graft function was administered antithymocite globulin in duration of 7-14 days, prophylactically. In 3 (6.97%) patients graft loss was caused by vascular complications and in 1 (2.32%) by infection as the complication. During the first post-transplantation year acute rejection was noticed in 8 (34.7%) patients and in 3 (37.5%) it was steroid resistant. The graft loss was never caused by acute rejection. Six-months graft survival was noticed in 91.1% patients and one-year graft survival in 88.4% patients. One-year patient survival was 100%. Short term results in living related kidney transplantation are excellent and nowadays, due to improvement in immunosuppressive therapy, the success in this type of kidney transplantation is mainly limited by surgical and infective complications.

Disease modifying and immunomodulatory effects of high dose 1 alpha (OH) D3 in rheumatoid arthritis patients.

OBJECTIVE: Vitamin D analogues such as 1 alpha (OH) D3 (alphacalcidiol) have a possible physiological paracrine effect on cell proliferation and differentiation. Experimentally established possibilities to prevent autoimmune diseases suggest that alphacalcidiol may have therapeutic value as an immunomodulatory agent in patients with rheumatoid arthritis. METHODS: We organized a 3-month open-label trial on 19 patients being treated with standard DMARD therapy for acute RA. They were divided into 2 subgroups, those with highly active RA and those with moderately active RA. Their regular drug regimen was maintained during the trial and oral alphacalcidiol 2 micrograms/day was added. Therapy results were evaluated by ESR, CRP, morning stiffness, the Richie index, and the Lee index. Immunomodulatory effects were investigated by measuring lymphocyte proliferation and apoptosis both in the patients and in vitro in 10 nM alphacalcidiol-supplemented culture medium. RESULTS: After 3 months, high dose oral alphacalcidiol therapy showed a positive effect on disease activity in 89% of the patients (45% or 9 pts. with complete remission and 44% or 8 pts. with a satisfactory effect). Only two patients (11%) showed no improvement, but no new symptoms occurred. No side effects were observed. CONCLUSION: These results suggest that alphacalcidiol is a powerful immunomodulatory agent with fairly low hypercalcemic activity. Clinical improvement was strongly correlated with the immunomodulating potential of this agent. We noticed dual effects on lymphocyte proliferation and apoptosis according to the prior cell activation state. Alphacalcidiol could therefore possibly be used as an adjunct therapy with DMARDs in patients with rheumatoid arthritis.

A dental implant: aluminium trioxide exhibited no effect on mouse reproductive and mutanogenic potential.

Several diseases as well as trauma can affect the composition and integrity of periodontal tissues leading eventually to the destruction of connective tissue matrix and cells, loss of attachment and resorption of alveolar bone, often followed by tooth loss. Replacement of the missing tooth could then be provided by endosseous dental implants healing in a form of osseo- or fibrosteal integration to the alveolar bone. Aluminium oxide ceramics, a form of endosseous implant, allows osseointegration type of healing and has demonstrated excellent biocompatibility. However, potential aluminium toxicity has been implicated in the pathogenesis of a number of clinical disorders and for this reason we examined the reproductive and mutagenic effect of aluminium trioxide ceramic implant in experimental mice. 720 female and 45 fertile male BALB-cAn NCR mice were included in the study. 3 experimental groups of fertile male mice (15 for each group) were treated with an intraperitoneal injection of aluminium trioxide (1 g/ kg of body weight, group I), with ethyl-methane-sulphonate as a positive control (200 mg/kg, group II) and with Tween-80 (10 mg/kg as a negative control, Group III). Each of the labeled male mice fertilized previously uncoupled female mice during 8 weeks (a pair per week) to facilitate appropriate pre- and post-meiotic conditions of spermatogenesis to occur. Female mice were sacrificed with cervical dislocation at day 13 after fertilization. Immediately upon sacrifice the uterus was removed and the number of alive and healthy, or alive but mutated and/or dead embryos was computed to determine the dominant lethal or mutagenic effect. Animals treated with aluminium trioxide demonstrated similar effects on the reproductive and mutagenic capacity as the negative control, whereas the animals treated as positive controls exhibited significantly reduced reproductive and mutagenic capacity. Collectively, we concluded that aluminium trioxide has a very low rate of embryonal mortality and mutagenicity in mice. This finding is in general agreement with the biocompatibility of aluminium trioxide as an implant material.

Bidirectional interactions between thymocytes and thymic epithelial cell lines in vitro.

In vitro interactions of thymocytes and thymocyte hybridomas with cortical (R-TNC.1) and medullary (TE-R 2.5) rat thymic epithelial-cell (TEC) lines were studied. It was found that the cortical line had better adhesion capability. It bound exclusively immature CD4+ CD8+ alpha beta TCRlo thymocytes, induced apoptosis of a subset of these cells, and stimulated proliferation of the BWRT 1 (CD4- CD8- alpha beta TCR-) hybridoma. The medullary line bound both immature and mature thymocytes, decreased their apoptosis, and induced apoptosis of the BWRT 8 (CD4+ CD8lo alpha beta TCRhi) hybridoma. Thymocyte differently modulated cytokine production by TEC lines, upregulating the secretion of IL-1 by R-TNC.1 and IL-6 by TE-R 2.5 cells. Finally, coculture of thymocytes with TEC lines resulted in different patterns of protein-tyrosine phosphorylation in thymocytes. These results show the existence of mutual bidirectional interactions between thymocytes and TEC lines in vitro, but these processes differed depending on phenotypic characteristics and origin of TEC lines used.

[Cyclosporin A in the treatment of Behçet's disease]. / Primena ciklosporina A u lecenju Behçet-ove bolesti.

The results of Cyclosporin A treatment of 15 patients with Behçet's disease were examined in the study--9 females (aged from 32 to 34 years, mean 33 years) and 12 males (aged from 25 to 55 years, approximately 34.33 years). Among them, the majority were with chorioretinitis (10/15 or 66.6%). Besides chorioretinitis two patients were simultaneously with iridocyclltis, while in three the whole nervous system was affected (meningoencephalitis, simultaneously pyramidal syndrome with the signs of extrapyramidal lesion and consciousness disorder in one patient). In one patient myocarditis was revealed, and the one was with deep aphtous ulcer. The approximate daily dose was 5 mg/kg in 13 patients, and 7.5 mg/kg/d in 2 patients. For that, the level of the drug in blood elevated from 79 to 380 ng/ml, approximately 170 ng/ml. The effect was favourable in 12 patients (complete restraint of the disease evolution), partial in 2 patients (slowing of the disease course) while it was incomplete in one patient for the interruption of the therapy 15 days after its beginning.

[Repair of a severed nerve with denatured muscle graft--preliminary results of a new surgical technic]. / Reparacija neurotmeza denaturisanim misicnim graftom--preliminarni rezultati nove operativne tehnike.

In Neurosurgical Clinic of Military Medical Academy prospective study about the use of denatured muscle graft in nerve repair is in progress, based on numerous experimental and sporadic clinical literature data. The first, experimental part of the investigation is directed to operative technique details and also to find out the manner and duration of muscle denaturation which provide ideal conditions for regenerating axons sprouting. It is concluded that greater pectoral muscle have to be muscle graft donor for nerve defects shorter than 6 cm, and sartorius muscle for those longer than 6 cm. Denaturation for 30 seconds in liquid nitrogen and after that in distilled water for 3 minutes results in micromorphological status in muscle graft which is optimal for axonal regeneration. In the second, clinical part of the work reparations of missile neurotmesis of radial nerve with denatured muscle grafts are performed. Preliminary results 9 months after operation are quite comparable with results after sural nerve graft reparation.

Aberrant levels of cytokines within the healing wound after burn injury.

OBJECTIVE: To study the effect of a burn injury on the course of cellular and cytokine changes in a wound and the relationship of these cytokines to the amounts of protein and collagen deposited at the site of the wound. DESIGN: A randomized control trial was done in which one group of rats were subjected to a severe burn injury. With the use of a sponge matrix model, the wound-healing parameters were evaluated. MATERIALS: A random sample of eight inbred albino Oxford rats per group were used in all experiments. INTERVENTIONS: Rats were subjected to a severe scald injury. Polyvinyl sponges were used as the wound-healing model. MAIN OUTCOME MEASURE: The obtained results implied that the wound-healing process is impaired after a severe burn injury. RESULTS: The wounds in these animals with burn injuries contained a lower number and an altered type of infiltrating cells with aberrant levels of cytokines, higher levels of interleukin-6, and lower levels of tumor necrosis factor and interleukin-1 in the fluids of the wounds. The parameters of healing (amounts of protein and collagen deposited at the site of the wound) were significantly lower in animals with burn injuries on days 7 and 14. CONCLUSION: The underlying mechanism of the impaired healing of a wound after burn injury could lie in the altered migration of inflammatory cells to the site of the wound and in the aberrant cytokine levels within the wound.

Adhesion molecules involved in the binding and subsequent engulfment of thymocytes by a rat thymic epithelial cell line.

A rat thymic epithelial cell (TEC) line (R-TNC.1) was established from a long-term TEC culture. Based on its ultrastructure, phenotype and cytokeratin profile, this line was characterized as a type of cortical TEC. R-TNC.1 cells had nursing activity which was manifested by the binding and subsequent engulfment of thymocytes. The role of adhesion molecules involved in these processes was studied extensively using a coculture of resting thymocytes and unstimulated or interferon-gamma (IFN-gamma)-stimulated R-TNC.1 cells. It was found that a number of adhesion molecules, such as CD2, CD4, CD8, LFA-1, CD18, ICAM-1 and Thy-1, was partly involved in the nursing activity. The effect of monoclonal antibodies (mAb) to these molecules depended on the incubation time and stimulation of R-TNC.1 cells. The inhibitory effect of mAb to CD2, LFA-1, CD18 and ICAM-1 on thymocyte engulfment was higher than their effect on thymocyte binding to the R-TNC.1 line. In addition, a LFA-1/CD18-dependent/ICAM-1-independent adhesion pathway was identified when unstimulated R-TNC.1 cells with minimal expression of ICAM-1 were used. The combination of inhibitory mAb did not completely abrogate the nursing activity of the R-TNC.1 line, suggesting the possible involvement of some other adhesion molecules.

Post-traumatic activation of draining lymph node cells. II. Proliferative and phenotypic characteristics.

Proliferative and phenotypic characteristics of cells in regional lymph nodes that drain burn injury were examined in rats on day 3 postburn, i.e. at the time of maximal spontaneous proliferation and of interleukin-2 and accessory cytokine (IL-1 and IL-6) production. The importance of IL-1 in spontaneous proliferation of draining lymph node cells was demonstrated by stimulation of IL-2-driven proliferation by recombinant IL-1 in vitro and by susceptibility of unstimulated proliferation to anti-IL-1 antibodies, while requirements for IL-6 in draining lymph node cell proliferation were less pronounced. Cell surface phenotyping revealed a slightly increased percentage of CD25+ cells in the blast cell population of freshly isolated draining lymph node cells after injury, which increased further during cultivation. Enrichment in CD8+ cells on day 3 following burn injury was demonstrated, while no changes in total cell population and CD4+ cells was noted. This was however preceded by pronounced percentual decrease of total T cells and CD4+ cells and by increases of B cells and MHC class II+ cells on day 1 postburn. Inhibition of draining lymph node cell proliferation by anti-MHC class II antibodies suggested that this proliferation was class II MHC dependent. The contribution of cell proliferation and/or cell influx to day 3 postburn draining lymph node cell activity is discussed.

A novel anti-rat CD18 monoclonal antibody triggers lymphocyte homotypic aggregation and granulocyte adhesion to plastic: different intracellular signaling pathways in resting versus activated thymocytes.

We have raised a monoclonal antibody (mAb), NG2B12, directed against rat CD18, capable of inducing lymphocyte homotypic adhesion and granulocyte adherence to plastic. NG2B12-induced aggregation is temperature sensitive and requires metabolic energy, an intact cytoskeleton and the presence of Mg2+, but is independent of protein synthesis. Ca2+ is not only dispensable but exerts a suppressive effect on the NG2B12-induced adhesion. The adhesion is readily observed in thymocytes and concanavalin A blasts of thymocytes and splenocytes but is very weak in resting spleen and lymph node cells. NG2B12 also enhances phorbol 12-myristate 13-acetate (PMA)-induced aggregation in an additive fashion. The NG2B12-induced homotypic adhesion is mediated by LFA-1. mAb against ICAM-1 completely inhibited the induced adhesion of activated cells but inhibited only partially and in a time-dependent manner the adhesion of resting thymocytes. The activation of protein phosphatases 1 and 2A (as assessed by the use of okadaic acid) is necessary for the NG2B12-induced adhesion of both resting and activated thymocytes. In contrast, H-7 (an inhibitor of protein kinase C and A), substantially suppressed the adhesion of resting thymocytes, whereas W-7 (an inhibitor of calmodulin-dependent protein kinase) inhibited the adhesion of activated thymocytes. NG2B12 induces both adherence to plastic and homotypic aggregation of granulocytes; the events being blocked by anti-CD18 (WT.3) and anti-CD11b/CD11c (OX-42) mAb, augmented by okadaic acid and not modified by H-7 and W-7. Additionally, we have demonstrated that NG2B12 and PMA employ distinct intracellular signaling pathways in inducing adhesion of both thymocytes and granulocytes.

[IL-1, TNF and IL-6 production by alveolar mononuclear cells in patients with sarcoidosis]. / Stvaranje interleukina-jedan, faktora nekroze tumora i interleukina-sest od strane alveolnih mononuklearnih celija kod bolesnika sa sarkoidozom pluca.

Cytokines produced by locally activated T cells and macrophages have central role in lymphocyte alveolitis and granuloma formation, and it is beleived that they regulate activity and further progression of sarcoidosis. The aim of our study was to evaluate the levels of interleukin-1 (IL-1), tumor necrosis factor (TNF) and interleukin-6 (IL-6) production by bronchoalveolar mononuclear cells in 6 patients With sarcoidosis. The obtained results showed increased IL-6 levels in patients with active disease, IL-1 activity did not follow clinical changes, while TNF was detectible only in one patients.

[Diagnostic problems of Stevens-Johnson syndrome. A case report]. / Stevens-Dzonsonov sindrom u decjem dobu. Znacaj imunoloskih parametara u dijagnostici i tumacenju patogeneze (prikaz bolesnika).

Stivens-Johnson Syndrome is a rare, severe, bullose form of erythema multiforme of unknown etiology. The role of immunological factors in its pathogenesis elucidates. A patients (Sh.V.), nine years of age, was admitted for reccurent streptococcal infections with skin and mucose membrane lesions. In June 1990 streptococcal pharyngitis, fever (38.8-39,9 degrees C) were registered. Penicillin was given. Next day bullous lesions on lips, left ear, trunk and lower extremities and vesiculose lesions with a wide, erythematose base ("iris") and then conjuctivitis were registered. Laboratory tests: SR70.; Leu - 11,0; anti-herpes Ab IgG 1/64, IgM 1/8. Stevens-Johnson was diagnosed. There was a recidivation two years after - oral lesions followed by necrosis and bleeding, after half a year a second recidivation with spreading of bullous and vesiculous lesions to penis gland with prepuce of the penis. Last recidivation in February 1993. Anamnesis: Viral meningitis in 1988. mother suffers from herpes labialis. Peripheral blood immunophenotiping lymphocite extremly indicated decreasing values of B Ly, NK and IL-2R+ cells. Bacteriological tests showed an increase of anti-Chlamidia Ab titer (IgG 1/128, IgA and IgM +). In virological testing there was no increase of titer of Abs against viral antigens (Herpes simplex virus, Varicella-Zoster virus, Citomegalovirus, Adenovirus). We conclude that Stevens-Johnson Sy to be diagnosed by characteristic clinical features, aspecialy by frequent reccurences. Immunological testing during the last recidivation showed that parameters of humoral immune reactivity were within normal ranges while revealed defects of cellular immune reactivity cannot elucidate the ethiopathogenesis of this disease.

An adhesion-promoting anti-rat CD18 monoclonal antibody differentially alters thymocyte responses to various mitogens.

Leukocyte function-associated antigen (LFA)-1 represents one of the major lymphocyte adhesion molecules being capable of both strengthening cell-cell contacts and cooperating with other relevant surface molecules in signal transduction. We have studied the effects of an adhesion-promoting anti-CD18 monoclonal antibody (mAb) (NG2B12) on thymocyte proliferation induced by various mitogens. As we have recently described, the adhesion-promoting function of this mAb strictly depends upon the activation of several intracellular protein kinases and phosphatases. In the present work we have found that NG2B12 inhibits concanavalin (Con) A-induced thymocyte proliferation suppressing IL-2 production by these cells. Conversely, this mAb enhances proliferative responses of thymocytes to phytohemagglutinin (PHA) and interleukin (IL)2 alone or in combination with the phorbol ester PMA. The effects of this mAb were compared with those of another anti-rat CD18 mAb which potently blocks the LFA-1/Intercellular adhesion molecules (ICAMs) interactions.

Distinct spectrum of N-ras mutations in aml and mds patients in yugoslavia.

Mutations that activate ras genes were demonstrated to be associated with certain types of malignancies. Multiple point mutations were predominantly found in the N-ras and occasionally in the K-ras genes. The analysis of 4 MDS, 23 AML and 11 CML patients from Yugoslavia revealed the prevalence of the N-ras mutation (83%) over K-ras mutations (17%). Although the frequencies of the N- and K-ras mutations in these patients were similar to the ones reported for patients from USA and Japan, the N-ras mutational spectra considerably differed. The prevailing type of mutation in patients from Yugoslavia was G-to-T transversion at the first position in the codon 12 of the N-ras gene. This study supports a hypothesis that different geographical and environmental factors may cause the accumulation of different type of point mutations in the same target gene.