Experimental studies have shown that IL-2 may antagonize chemotherapy-induced lymphocytopenia. On this basis, we have evaluated the influence of low-dose IL-2 on lymphocyte and NK cell numbers in cancer patients treated with the anthracycline drug, epirubicin. The study included 7 metastatic breast cancer women treated with epirubicin at a dose of 25 mg/m2 i.v. weekly. IL-2 was given subcutaneously at 3 million IU/day for 6 days/week. Venous blood samples were drawn at weekly intervals, and the results were compared to those seen in 14 patients treated with epirubicin alone. Lymphocyte mean number observed on treatment was higher in patients concomitantly treated with IL-2 than in those receiving epirubicin alone, without, however, significant differences. In addition, NK cell mean number was significantly higher in patients receiving IL-2 than in those treated with epirubicin alone. These preliminary results would suggest that IL-2 may antagonize lymphocyte and NK cell declines during cancer chemotherapy with anthacyclines. Further studies will be required to confirm these results and to establish their possible influence on chemotherapy-induced tumor regressions.