Fifty-three patients with AIDS-related Kaposi's sarcoma and no previous treatment with cytotoxic chemotherapy enrolled in a phase II multicenter study to evaluate the safety and efficacy of weekly doxorubicin treatment. Doxorubicin was given intravenously at a dose of 15 mg/m2. Patients were stratified for purposes of analyses by tumor burden and coexistence of HIV-associated signs and symptoms; stratum I included patients with cutaneous disease alone and no symptoms, and stratum II included patients with visceral disease, tumor-associated edema, a previous opportunistic infection, or systemic symptoms. Fifty-one patients were evaluable for toxicity and 50 for tumor response. Five patients had a partial response (10%); 32, a minor response (64%); 12, no change (24%); and one, progression (2%) as the best measurable response. Partial response durations ranged from 4 to 14 weeks. Fifteen patients subsequently showed progression while on treatment. A significantly greater number of patients in stratum I (20.1%) had a partial response compared with those in stratum II (0%, p = 0.009). The major toxicities included nausea (37%), stomatitis (9.8%), mucositis (13.7%), and moderate to severe neutropenia (71%). Neutropenia was dose limiting and resulted in discontinuation of doxorubicin in 18% of the patients. Two patients developed cardiac toxicity. In conclusion, doxorubicin treatment induced relatively few tumor responses and remission durations were short. Treatment was limited by a high rate of toxicity.