Because two of five patients with renal cell carcinoma in a Phase I study had partial response to recombinant alpha-2 interferon (IFN), we treated 26 patients with advanced renal cell carcinoma with a 3-month regimen of IFN. Patients were randomized to receive IFN either subcutaneously (2 X 10(6) IU/m2 3 times a week) or intravenously (3 X 10(7) IU/m2 for 5 consecutive days every 2-3 weeks). Patients whose disease was responding or stable were treated further, while those with progressive disease on subcutaneous treatment were offered intravenous therapy. Sites of metastasis included lung (14 patients), bone (7 patients), soft tissue (7 patients) and liver (2 patients). Twenty patients were evaluable for response. One patient had a partial response at the end of the third course of intravenous IFN and subsequently had complete disappearance of a 12 X 7 cm subcutaneous mass after the seventh course of treatment. The disease was stable in 13 patients including two minor responses, and six patients had progressive disease (5 with subcutaneous treatment; 1 with intravenous treatment) including one mixed response. All patients experienced early flu-like symptoms of fever, chills, and rigors during the first few days of treatment and most had mild to moderate fatigue. Three patients left the study because of fatigue, and one had an urticarial rash. From these results and our previous experience, it appears that IFN has activity against renal cell carcinoma with acceptable toxicity.