A pilot study was undertaken to evaluate toxicity and activity of recombinant alpha-2b interferon in patients with metastatic malignant melanoma. Interferon was administered at the dosage of 10 x 10(6) IU/m2, 3 times a week i.m. 21 patients entered the study, 17 pretreated with chemotherapy and/or immunotherapy and 6 untreated. We obtained 3 partial responses (14.3%; 95% CL, 3.0-36.3%); 9 patients had stable disease. All patients experienced flue-like symptoms and fever; most fatigue and worsening of performance status. Recombinant interferon alpha-2b at the dosage and schedule used has limited but definite activity in metastatic malignant melanoma; the substantial subjective toxicity must be taken into consideration. Further trials testing recombinant alpha interferon in combination with chemotherapeutic agents, like DTIC, are warranted.