195mPt-labeled cisplatin was administered iv and ip to control mice and to mice bearing Sarcoma 180. The delivered dose was 8 mg/kg and the injected activity was 80 muCi/kg. Whole-body autoradiography was performed at various times after treatment. For all animals, concentration of radioactive material was observed in the kidneys as early as 5 minutes after treatment. Most of the delivered radioactivity was present in the urine-bladder for the first 4 hours after the injection. Autoradiography also showed concentration of 195mPt in the bile ducts. These results suggest that a lower but significant part of the delivered radioactivity was also eliminated in the bile, which may explain in part the presence of the isotope in the gut lumen. In addition, 195mPt-equivalents were observed in the kidney parenchyma, the cartilages, the teeth, the skin, and the hair. Only trace amounts of 195mPt were present in the hypophysis and the testes. The distribution of radioisotope in healthy and tumor-bearing animals was comparable. Measurable uptake occurred in the Sarcoma 180 tumor.