We conducted a phase II trial to confirm the activity of fixed, low dose gamma-interferon in metastatic renal cell carcinoma. A total of 35 patients with metastatic renal cell carcinoma, who had not received prior immunotherapy and who had a Zubrod performance status of 2 or less, was enrolled in this study. Primary tumors were controlled by nephrectomy or embolization before treatment began. gamma-Interferon was administered weekly as a subcutaneous injection at a fixed dose of 100 micrograms. Toxic effects were limited to low grade fever, chills and myalgias within 24 hours of injection. There were no incidences of grade 3 or 4 toxicity. Responses could be evaluated in 34 patients. There were 1 complete and 4 partial responses, for an objective response rate of 15% (95% confidence interval 5 to 32%). Durations of response to date are 21+, 17+, 13+, 9 and 2 months. We conclude that gamma-interferon is an active agent for metastatic renal cell carcinoma when administered according to this dose and schedule. The response rate compares favorably with those of alpha-interferon and interleukin-2, and toxicity is minimal. gamma-Interferon has excellent potential for use in combination with other biological or chemotherapeutic agents and in the adjuvant setting.