Between October 1987 and November 1988, 95 European patients with metastatic renal cell carcinoma have been treated with recombinant interleukin-2 (rIL-2) (EuroCetus) at 18 X 10(6) IU/m2/day (equivalent to 3 X 10(6) Cetus Units/m2/day) according to the West schedule in two trials. 1. Forty-two patients received rIL-2 alone. Median time between initial diagnosis and metastases was three months. Eighty-one percent of the patients had at least two involved sites at inclusion and 86% underwent prior nephrectomy. Twenty-seven patients (64%) received two successive courses. Over 80% of the planned dose was administered in 69% and 44% of patients during courses 1 and 2, respectively. Fever, hypotension, weight gain, rise in creatinine level, hepatic disturbances, anaemia and thrombocytopenia were commonly observed but resolved promptly after completion of therapy. No toxic death was recorded. Two (6%) complete responses (CR), four (13%) partial responses (PR), four stable diseases (SD) and 22 progressive diseases (PD) were observed. The response rate is 6/32 (19%); the median progression-free survival time is not reached at 218+ days (92-394). 2. Fifty-three patients received rIL-2 with lymphokine-activated killer (LAK) cells. Median time from primary diagnosis to metastases was three months. Eighty-five percent of patients had at least two involved sites though 73% had previously undergone nephrectomy. Forty patients (75%) received two successive induction courses. Most patients, i.e. respectively, 77% and 60%, were given at least 80% of the planned dose during courses 1 and 2. Median numbers of LAK cells infused were 13.1 and 11.6 X 10(9) nucleated cells per course, respectively. Toxicity was not different from that described above; no toxic death occurred; five CR (10%), nine PR (18%), 11 SD and 26 PD were observed. The response rate is 14/51 (27%) and the median progression-free survival time is not reached at 7.2+ months (3-13.1). In conclusion, rIL-2, with or without LAK cells, is obviously active on metastatic renal cell carcinoma. The difference in response rate between the two trials is not statistically significant but has to be paralleled with the difference in dose received by the patients rather than with the addition of a cellular therapy. Toxicity was always manageable and reversible. The association of rIL-2 with other lymphokines should represent a major issue to improve the response rate and will be considered in further European studies.