To minimize interleukin-2-related toxicity while retaining its efficacy, a treatment schedule utilizing subcutaneous IL-2 was evaluated in a phase II setting. Eighty unselected, consecutive patients with metastatic or recurrent renal cell carcinoma (RCC), mean age 58 years (range, 21 to 76), received IL-2 on an outpatient basis, 5 days per week for 4 or 6 consecutive weeks. During the first 5-day cycle, a dose of 18 million IU IL-2 was administered once a day; during subsequent cycles the dose in the first two days was reduced to 9 million IU. Two 6-week or three 4-week courses were given maximally. Patients who had completed at least one full course were considered evaluable. To circumvent flu-like symptoms, all patients received a maximum oral dose of 3 g acetaminophen daily. Seventy-seven patients were assessable for response. Three (4%) complete responses (CR) and 6 (8%) partial responses (PR) were observed, and 44 (57%) patients had stable disease (SD). Response durations were 64, 29, 29+ months for the CR and 2, 6, 8, 11, 32, 47 months for the PR. The median length of survival of all patients was 12 months, whereas the median survival of responders and non-responders was 35+ and 10+ months, respectively (P < 0.001). Side effects included fever, chills, nausea, vomiting, and transient inflammation and induration at the injection sites. These complications were acceptable, even in the patients with concomitant disease, and completely disappeared after cessation of IL-2. Subcutaneous IL-2 mediates antitumor responses, has limited side effects and is also suitable for elderly RCC patients with concomitant disease.