In an ongoing cooperative study of the Cancer and Acute Leukemia Group B, 21 evaluable patients with advanced malignant lymphomas were treated with 70 mg/m2 of cis-dichlorodiammineplatinum(II) (cis-platinum) once every 3 weeks. All patients had received extensive prior therapy. Partial remission was obtained in two of seven patients with Hodgkin's disease, for 1+ and 7 months, and in three of 14 patients with non-Hodgkin's lymphoma, for 2, 2+, and 2.5 months. In another ongoing trial, 11 patients with advanced, pretreated small cell cancer of the lung received 80 mg/m2 of cis-platinum once every 3 weeks. Four patients achieved partial remissions. These lasted 2+ and 2.5 months in the two patients evaluable for duration of response. Two further clear-cut tumor regressions were noted. The major toxic effects were myelosuppression and vomiting. In the second trial, one case of probable drug-related fatal nephrotoxicity was encountered despite optimal forced diuresis with mannitol and furosemide. cis-Platinum definitely warrants further evaluation in these diseases because of significant effectiveness even after extensive prior treatment.