The purpose of this study was to evaluate in a randomized phase II trial the efficacy and toxicity of combination biochemotherapy compared with chemotherapy alone in patients with metastatic melanoma. Sixty-five patients with metastatic melanoma (ECOG performance status 0 or 1) were randomized to receive intravenous BCNU 100 mg m(-2) (day 1, alternate courses), cisplatin 25 mg m(-2) (days 1-3), DTIC 220 mg m(-2) (days 1-3) and oral tamoxifen 40 mg (BCDT regimen) with (n = 35) or without (n = 30) subcutaneous interleukin 2 (IL-2) 18 x 10(6) iu t.d.s. (day - 2), 9 x 10(6) iu b.d. (day - 1 and 0) and interferon 2 alpha (IFN-alpha) 9 MU (days 1-3). Evidence for immune activation was determined by flow cytometric analysis of peripheral blood lymphocytes. Treatment was repeated every 4 weeks up to six courses depending on response. The overall response rate of BCDT with IL-2/IFN-alpha was 23% [95% confidence interval (CI) 10-40%] with one complete response (CR) and seven partial responses (PR), and for BCDT alone 27% (95% CI 12-46%) with eight PRs; the median durations of response were 2.8 months and 2.5 months respectively. Sites of response were similar in both groups. There was no difference between the two groups in progression-free survival or overall survival (median survival 5 months for BCDT with IL-2/IFNalpha and 5.5 months for BCDT alone). Although 3 days of subcutaneous IL-2 resulted in significant lymphopenia, evidence of immune activation was indicated by a significant rise in the percentage of CD56- (NK cells) and CD3/HLA-DR-positive (activated T cells) subsets, without any change in the percentage of CD4 or CD4 T-cell subsets. Toxicity assessment revealed a significantly higher incidence of severe thrombocytopenia in patients treated with combination chemotherapy than with chemotherapy alone (37% vs 13%, P = 0.03) and a higher incidence of grade 3/4 flu-like symptoms (20% vs 10%) and fatigue (26% vs 13%). The addition of subcutaneous IL-2 and IFNalpha to BCDT chemotherapy in a randomized phase II trial resulted in immune activation but did not improve response rates in patients with metastatic melanoma, and indeed may increase some treatment-related toxicity.