RESUMEN
Superficial Ehrlich tumours in mice were used to assess how much information on cell kinetics could be obtained from only the simplest techniques of autoradiography, and in situ monitoring of 125I-iodo-deozyuridine. These techniques were selected as being readily applicable to clinical situations. Intradermal tumours were studied from the earliest stages of rapid growth to large slow growing tumours with necrotic cores, as well as tumours undergoing regression. For comparison, intramuscular tumours were studied with systemic injections of radioactive DNA precursors. It was found that extensive information on cell production and loss rates was obtained from a single injection of tritiated thymidine followed by a single biopsy, or alternatively in vitro labelling of one minute biopsy specimen, and measurements of only the labelling index, together with a knowledge of the tumour's growth characteristics. Following a single localized injection of 125I-iodo-deoxyuridine, the loss rate of radioactivity measured in situ for a period of about 1 week provided an index of cell loss rate from the tumours.