The present phase II study was undertaken to assess antitumoral activity, safety and tolerability of recombinant human interleukin-6 (rh IL-6) in patients with advanced renal cell cancer. Rh IL-6 was administered as a daily subcutaneous injection at a fixed dose of 150 micrograms/day for a maximum of 42 consecutive days. 12 patients with metastatic renal cell cancer without previous immunotherapy were enrolled and were evaluated for response. No objective clinical responses were observed in the trial. Toxicity was moderate and reversible and mainly comprised fever, influenza-like symptoms, fatigue and moderate hepatotoxicity. Anaemia, leucocytosis, thrombocytosis and induction of an acute phase response were observed in most patients. In conclusion, prolonged subcutaneous administration of rh IL-6 on an outpatient basis is safe and feasible. However, rh IL-6 exhibited no antitumoral activity in patients with metastastic renal cell cancer. Profound regulatory effects on haematopoiesis and inflammatory response of rh IL-6 were observed.