High-dose therapy with interleukin-2 (IL-2) can produce significant responses in patients with metastatic melanoma (MM) and renal cell carcinoma (RCC). Several studies have shown the benefit of low-dose IL-2 in patients with RCC, but few studies have evaluated low-dose IL-2 in MM. We have used the following regimen: Interferon-alpha 10 million units subcutaneously on days 1, 3, 5, 8, 10, 12, 22, 24, and 26; and IL-2 60,000 IU/kg i.v. every 8 h on days 8-12 and 22-26. Patients had measurable MM or RCC and were excluded for ECOG status > 3, brain metastases, or significant cardiopulmonary or renal dysfunction. Between January 1993 and April 1996, 38 patients with MM and 14 with RCC were treated. In MM, there were six responses (15.7%; 95% confidence interval 4.1-27.3%) (i.e., one complete response and five partial responses). Responses were seen in visceral and nodal disease. Responses were of good duration: 40+, 26+, 13, 6, 4, and 3 months. One response was seen in the 14 RCC patients. Treatment was considerably less toxic than with high-dose IL-2. All treatment was given in a medical or surgical ward with intensive care necessary in only two patients. More than 80% of patients received > 80% of the predicted dose of IL-2. Dose-limiting toxicity consisted mainly of mild confusion or fatigue. In summary, this regimen is better tolerated and produces response rates within the range reported for high-dose IL-2 for patients with MM.