Single-agent intravenous vinblastine, 4 to 8 mg/week, was used to treat 38 patients with Kaposi's sarcoma related to the acquired immunodeficiency syndrome. The dose was titrated in relation to the total leukocyte count. Ten patients had an objective response, and 19 had stable disease during therapy. Apart from expected modest neutropenia, toxicity was minimal. A lower response rate was seen in patients with anemia, an elevated erythrocyte sedimentation rate, or any lymphoma-like B symptom. Opportunistic infections were common regardless of type of response but were commoner in patients who did not respond. Vinblastine used in low doses weekly is effective in treating Kaposi's sarcoma related to the acquired immunodeficiency syndrome and has minimal associated toxicities.