Cisplatin was given intravenously to 35 evaluable patients with unresectable malignant mesothelioma on Southwest Oncology Group (SWOG) Study 8418. Five patients (14.3%) achieved partial response with median response duration of six months (range 2-12 months); eleven patients (31.4%) had stable disease of median duration of 5.5. months (range 2-21 months). Median survival for all patients was 7.5 months, 9 months for responders. Toxicity was as expected except that 12 patients (34.2%) discontinued cisplatin because of side effects. Cisplatin has moderate activity in mesothelioma and further studies with platinum analogues should be pursued.