Because Cisplatin potentiates the effect of radiotherapy in animal tumor systems and because Cisplatin is capable of causing regressions of human malignant melanomas, a study was initiated in patients with malignant melanoma metastatic to brain to investigate the feasibility of administering Cisplatin once a week during cranial irradiation. Cisplatin 40 mg/m2/week (three doses) was given I.V. to 18 patients during whole brain irradiation, 3 000 rads in 12 fractions over 21/2 weeks. Eleven patients also received Cisplatin 120 mg/m2 every three weeks, starting three weeks after cranial irradiation. Median survival was ten weeks, and only one of 13 patients whose brain metastases had not been resected experienced neurological and CT scan improvement. Thirteen patients have died, and brain metastases were a major cause. No regression of extracerebral tumor was seen in 15 patients with evaluable extracerebral lesions. During weekly low-dose Cisplatin administration, nausea and vomiting were moderate to severe. No granulocytopenia was noted, although three courses were associated with mild thrombocytopenia. Mucositis, peri orbital swelling, vertigo, and headache were each noted in two of 51 courses of treatment and seizures, ototoxicity, pancreatitis, and hiccups were each noted in one course. Renal toxicity and ototoxicity each developed in three of the 11 patients receiving Cisplatin 120 mg/m2, and nausea and vomiting were severe.