Twenty-six patients with histologically proven metastatic malignant melanoma were included in a phase II trial of interferon alfa-2b (Intron A; Schering-Plough). Patients were given 10 X 10(6) IU/m2 of interferon alfa-2b subcutaneously three times a week until major intolerance or progression of disease. General signs of intolerance were seen in all patients; hematological toxicity with leukopenia (below 1,800/mm3) and/or thrombocytopenia (below 600/mm3) was seen in six patients and therapy was interrupted in one patient. Mild liver toxicity was seen in most patients after two weeks of treatment. These manifestations disappeared 1-2 weeks after treatment was discontinued. Twenty-four patients were evaluable for response. There were two complete responses; one skin and one lymph node going into remission for 12 and 12.5 months respectively. A partial response was observed in five cases lasting 1, 1.8, 2, 3 and 5 months respectively. These results indicate a potential role for interferon alfa-2b in treating patients with metastatic malignant melanoma, however, further trials are required to determine the optimum dose and schedule of administration and use of interferon alfa-2b in combination with cytotoxic drugs.