Fifty-nine patients with metastatic malignant melanoma were entered into a phase II trial of recombinant alpha-2 interferon given in a dosage of 10 million IU/M2 subcutaneously three times per week for one year. Forty-five of these were evaluable for response. Of five evaluable patients with ocular primaries, none responded to interferon treatment. Four of 40 patients (10%) with cutaneous primaries achieved complete remission, and 6 further patients (15%) had partial remissions for a combined response rate of 25%. Two patients remain in complete remission 15+ and 32+ months after starting treatment. Responses were limited to subcutaneous, lymph node and lung metastases. The treatment schedule was well tolerated with the majority of patients receiving more than 70% of their predicted doses. Flu-like symptoms were the most common side effect. No evidence of cumulative toxicity was seen. We conclude that interferon is an active agent in metastatic malignant melanoma of cutaneous origin and that further trials are indicated.