From May 1991 to January 1996, 54 patients with advanced malignant melanoma were enrolled into a phase II trial testing the new nitrosourea cystemustine, administrated intravenously as a 15 min infusion every 2 weeks at 90 mg/m2 for three cycles followed by 60 mg/m2. Out of the 54 enrolled patients, 10 were Ineligible, leaving 44 fully evaluable patients (World Health Organization criteria). Twenty one patients had already received first-line palliative chemotherapy and/or immunotherapy. The median age was 62 years (range 30-74 years) and the median performance status was 0 (grade 0, 19 patients; grade 1, 21 patients; grade 2, 4 patients). Five patients with partial responses (lasting 16-29 weeks, mean duration 24 weeks), nine with stable disease and 28 showing progression were observed, giving an overall response rate of 11% (confidence interval 3.8-24.6%). Toxicity was mild and consisted mainly of neutropenia (39% grade III-IV), thrombocytopenia (42% grade III-IV); febrile aplasia was rare. Cystemustine administered to this schedule appears to have limited clinical activity and acceptable toxicity in untreated or second-line advanced malignant melanoma.