Our group and others have conducted phase II trials of high-dose interleukin-2 (IL-2) or IL-2 with the adoptive transfer of in vitro activated lymphocytes in patients with advanced malignancies. Although durable complete and partial responses were seen in patients with renal cell carcinoma and metastatic melanoma, overall response rates were low and toxicity was substantial. In preclinical models, the combination of IL-2 and interferon-alpha has synergistic antitumor activity. Based on these data, and our prior experience with high-dose IL-2 (Cetus), we conducted a trial to determine the maximum tolerated dose of IL-2 (0.4, 0.8, and 1.2 mg/m2) administered together with a fixed dose of interferon-alpha 2b (3 x 10(6) u/m2) intravenously every 8 h on days 1-5 and 15-19. Patients were monitored in the intensive care unit and given pressor support for hypotension as needed. Twenty-four patients were entered (6, 10, and 8 at each IL-2 dose, respectively; 14 renal cell carcinoma, 7 melanoma, 2 colon, and 1 hepatoma). The median age was 56 years, the male to female ratio was 19:5, and performance status was 0 or 1 (Eastern Cooperative Oncology Group) in all patients. Toxicity was similar at all dose levels, but the onset was earlier in the treatment course as the dose of IL-2 was escalated in successive cohorts; therefore, more doses were withheld at the higher dose levels. The major toxicities resulting in the interruption or stopping of treatment were hypotension requiring pressors, dyspnea, and neurotoxicity. Grade 1 or 2 fever, nausea and vomiting, fatigue, and cutaneous reactions were common at all dose levels.(ABSTRACT TRUNCATED AT 250 WORDS)