Thirteen patients with metastatic melanoma and ten patients with advanced renal cell cancer (RCC) received interferon alfa-2a (Roferon-A) and vinblastine. In melanoma the interferon dose was 3-9 million IU i.m., escalated daily for 10 weeks, and in RCC the dose was 18 million IU three times a week i.m. The dose of vinblastine was 0.075-0.15 mg/kg every third week i.v. One of the ten evaluable patients with melanoma had partial remission (PR; 11%) and three presented no change (NC). Three of seven evaluable patients with renal cell carcinoma had PR (43%) and three NC. Duration of the remission was 10 months in the melanoma patients and 7+, 10+, and 7+ in the RCC patients. The three times a week schedule was better tolerated. The most common side effects were fever, fatigue, loss of taste, weight loss, and neutropenia. On the basis of these results it can be concluded that in melanoma the combination of daily administration of interferon and vinblastine is not effective, whereas in renal cell cancer interferon and vinblastine treatment given three times a week seems to be favorable.