The present study was designed in order to evaluate the response rate and the toxicity of continuous infusion of Interleukin 2 (IL2) in patients over 65 with metastatic renal cell carcinoma. Twenty-five patients, median age 69 (range 65-77), without any prior systemic anticancer therapy received a continuous infusion of IL2 at a dose of 18 x 10(6) iu m-2 d-1 for 2 periods of 5 days separated by a 6 day break. Toxicity was not different compared with younger patients (e.g. fever, hypotension, rise in creatinine level), except for cardiac toxicity which was of great concern. Despite normal cardiac tests prior to inclusion into the study, abnormalities of the cardiac rhythm ranging from tachycardia to ventricular extrasystoles occurred in 44% of the patients and IL2 cardiac toxicity was responsible for one toxic death. Three objective responses, i.e. one partial and two complete persistent responses, were seen in 22 evaluable patients. Thus, if age does not seem to modify the potential for response to IL2 therapy, cardiac toxicity appears as a limiting factor for intravenous schedules of IL2.