Phase I study of interleukin-2 and interferon alfa-2a as outpatient therapy for patients with advanced malignancy. Twenty-six patients were treated in this phase I study with the combination of interleukin-2 (IL2) administered as a continuous infusion and interferon alfa-2a (IFN alpha-2a) administered intramuscularly to patients in an outpatient setting. The maximum-tolerated dose of both agents given as outpatient therapy was 2 x 10(6) U/m2 days 1 to 5 of IL2 and 9 x 10(6) U/m2 days 1, 3, and 5 of IFN alpha-2a for 4 consecutive weeks. A 2- to 4-week rest period was permitted after each 4 weeks of treatment. Fatigue was the treatment-limiting toxicity, and serious clinical or laboratory abnormalities occurred infrequently during this study. Patients with colon cancer metastatic to the liver tolerated treatment worse than patients with other tumors. Twelve of the 15 patients with renal cell cancer were assessable for response determinations. Of these 12 patients, three exhibited complete tumor regression, three have had partial objective regression, and three patients experienced stabilization of rapidly progressive disease. This therapy appears to be well tolerated in an outpatient treatment setting and shows significant activity against advanced renal cell cancer. 