Eighteen patients with histologically documented small cell carcinoma of the lung who had failed initial combination chemotherapy regimens were treated with single-agent cisplatin in a dose of 100 mg/m2 every 3 weeks, with mannitol and fluid diuresis. Tumor regression was limited to one partial response (response rate, 6%; 95% confidence limits. 1%-27%). Significant toxic effects were gastrointestinal (severe nausea and vomiting in 12 of 14 patients) and hematologic (severe leukopenia in one patient and severe thrombocytopenia in three). The antitumor efficacy of high-dose cisplatin in heavily pretreated patients with small cell carcinoma of the lung appears to be marginal.