Pretreatment with a low dose of cyclophosphamide (CY) has been claimed to inhibit suppressor functions and augment various immune functions. A combination of a low dose of CY, alpha-interferon (IFN-alpha) and continuous infusion of interleukin-2 (IL-2) was used to treat patients with advanced renal cell cancer (RCC) (stage IV). Sixteen patients received four cycles consisting of CY (500 mg m-2) three days prior to daily i.m. injections of alpha-IFN (3 x 10(6) U), and continuous infusion of 18 x 10(6) IU rIL-2 for five days. The cycle interval was three weeks. Two patients had partial response (13%) (26+ and 12+ months), two had a minor response (9+ and 4 months), and three patients achieved stable disease (19+, 14+ and 8+ months). No patients required intensive care. Side effects were mainly fever, malaise, capillary leak syndrome and diarrhoea. Non-responders showed significantly higher eosinophil and platelet counts compared to responders. Serum concentration of IL-2 was significantly higher in responders. 5/11 patients had abnormally low values of serum thyroxine after therapy. Two patients needed thyroid hormone substitution. The difference between the initial and the lowest thyroxine values correlated significantly to survival (p < 0.03). The addition of CY to rIL-2 and IFN-alpha in the present protocol did not contribute to an increased major response rate.