Thirty-one patients with advanced malignant mesothelioma, previously untreated or having received only one prior cytotoxic regimen, were treated in a prospective, single-arm phase II trial with carboplatin (NSC 241240) at a dose of 150 mg/m2 per day intravenously (IV) for 3 days (450 mg/m2/course). One complete remission and four partial remissions were achieved, yielding an overall objective response rate of 16% (95% confidence interval [CI], 5.4% to 34%). The median duration of remission was 8 months (range, 5 to 17). Nonhematological toxicity was mild (only 12% with World Health Organization [WHO] grade 3 vomiting); 16% suffered WHO grade 3 to 4 hematological toxicity, but there were no life-threatening episodes and no treatment-related deaths. Carboplatin has modest activity against malignant mesothelioma and, because of its low toxicity, has a role in the management of this disease.