Immunologic monitoring of cancer patients treated with IL-2 might help to determine functions of significance for the clinical outcome. Some immune functions in patients with advanced renal cell carcinoma were studied during treatment with low dose cyclophosphamide, alpha-interferon and IL-2. Cyclophosphamide (500 mg m-2) was given day 1, and alpha-interferon (3 x 10(6) u i.m.) and continuous infusion of IL-2 (18 x 10(6) u m-2 day-1) for days 4-9. The cycle interval was 3 weeks. Two to six cycles were given. Eleven patients entered the study. One patient achieved a partial remission, two patients had a minor response and four had a stable disease ('responding patients'). NK cell activity (K562) increased in all patients while LAK cell activity (against a renal cell carcinoma cell line, A498) was significantly augmented only in responding patients. In the responder group, there was a significant increase in CD3+/HLA-DR+ T-cells. In parallel, there was a significant decrease in CD45RA+ cells as well as in the CD4/CD8 ratio. These data might indicate an expansion of activated T cells with a reduction of cells with a suppressor phenotype in responding patients. The results corroborate the importance of activation of LAK cells and T cells during IL-2 therapy of cancer patients.