Fifty patients with metastatic gastric cancer were entered for a phase II study of Cis-diamminedichloroplatinum (II) (CDDP), 45 of whom were able to have their responses evaluated. CDDP was given intravenously at a dose of 80 mg/m2 over two hours every three weeks. There were four partial responses (25%) among the 16 patients who had had no prior chemotherapy, and three partial responses (10%) among the 29 patients who had had prior chemotherapy. The total response rate was 16%. The chief manifestations of toxicity were gastrointestinal symptoms, such as nausea and/or vomiting. Severe nephrotoxicity was not observed. From these data, the administration of CDDP at a dose of 80 mg/m2 every three weeks was considered tolerable, and CDDP as a single agent was considered effective against metastatic gastric cancers. In addition, three of the 29 pretreated patients who responded suggested that CDDP could be given as a second-line chemotherapy when initial treatment with other active agents, i.e. fluorinated pyrimidine or mitomycin C, fails to obtain a response.