Based upon the in vitro synergistic activity of interferon-beta (IFN-beta) and interferon-gamma (IFN-gamma) observed in melanoma cells, we initiated a Phase II trial using the combination to determine the clinical antitumor efficacy in patients with advanced disease. Fifteen patients with metastatic malignant melanoma were given 2,000 micrograms of recombinant IFN-gamma (rIFN-gamma) (Biogen) intravenously (i.v.) over 10 min, followed by a 10 min i.v. injection of 30 million units of recombinant IFN-beta (rIFN-beta ser) (Triton) 3 x/week. Six patients had skin, soft tissue, nodal, or subcutaneous metastases, 6 had visceral disease only, and 3 had both. Seven patients had received prior treatment, including chemotherapy (6), radiotherapy (3), and/or immunotherapy (3). Side effects included typical IFN constitutional symptoms such as anorexia, fatigue, nausea, and myalgias, but were not dose limiting. The mean drop in the white blood cell count (WBC) following 1 month of therapy, compared to baseline, was 3.3 x 10(3)/mm2 (p = 0.002); the mean increase in SGOT was 24.1 U/l (p less than 0.001). One patient had a dose reduction for Grade III anorexia and fatigue which did not resolve with repeated treatment. One patient with liver metastases had radiographical and clinical stabilization of his disease for 1 year. No responses were seen. The median time to progression was 6 weeks. Two patients' tumors were evaluable in the human tumor colony forming assay (HTCFA) and were markedly sensitive to the antiproliferative effects of IFN combinations. Both patients, however, failed to respond clinically.(ABSTRACT TRUNCATED AT 250 WORDS)