The purpose of this multicentre phase II trial was to evaluate time to progression, survival time, rate of objective tumour response and toxicity of second-line intravenous treosulfan chemotherapy in stage IV melanoma patients. Thirty-one patients with measurable stage IV malignant melanoma and prior chemotherapy with a dacarbazine-containing regimen were included. Of this group, 26 patients were evaluable. All patients received treosulfan (8 g/m intravenously on day 1; cycle repeated every 28 days up to six courses). Patients were evaluated for tumour response, survival time and toxicity. No objective responses (complete or partial) were observed. Five patients (19%) showed no change and 21 had progressive disease after treosulfan treatment. Four patients experienced a minor or mixed response. The median time to progression was 1.8 months (95% confidence interval [CI] 1.6-2.1 months) and the median overall survival was 6.5 months (95% CI 3.1-10 months). The 1 year survival rate was 33.9% (95% CI 15.4-52.3%). Leukocytopenia and thrombocytopenia (Common Toxicity Criteria grades 3 and 4) occurred in 15% and 18% of cases, respectively. The non-haematological toxicity of this outpatient regimen was mild. In conclusion, intravenous treosulfan treatment does not induce objective response rates when used as a second-line treatment of metastatic malignant melanoma.