Carboplatin (400 mg/m2) was given at 28-day intervals to 41 patients with malignant mesothelioma. In all, 40 patients were eligible and evaluable for response. Partial responses were seen in 2 cases (5%); regression of evaluable disease, in 1 patient (2%); and stable disease, in 19 subjects (48%). A median of two doses of carboplatin per patient resulted in mild toxicity. Leukopenia (less than or equal to 2,000 cells/microliters) and thrombocytopenia (less than 100,000 cells/microliters) were seen in only 6% and 20% of the patients, respectively. Median survival from study entry was estimated at 7.1 months, with a 1-year survival of 25% +/- 7%. Carboplatin given at a dose of 400 mg/m2 at 28-day intervals shows minor activity against malignant mesothelioma.