Adoptive immunotherapy with recombinant interleukin-2 (rhIL-2) has been reported to induce tumour regression in some patients with refractory cancer. However, the cardiovascular toxicity of bolus therapy requires invasive monitoring of patients in the intensive care unit (ICU). In an effort to examine the haemodynamic alterations caused by a constant infusion of IL-2, as opposed to bolus therapy, we studied the haemodynamic variables of 10 patients, with no evidence of heart disease, receiving 3 x 10(6) IU/m2 per day of rhIL-2 as a continuous infusion for 5 days. Measured and derived haemodynamic variables were obtained immediately prior to, at 2, 24, and 48 h during, and upon termination of the infusion. There was no evidence of clinical haemodynamic instability in these patients. Except for development of fever and tachycardia, there were no clinically significant differences in any measured or derived haemodynamic parameter. Moreover, continuous electrocadiographic monitoring of these patients during the infusion did not reveal any abnormalities. Invasive haemodynamic monitoring in an ICU is not necessary in carefully selected patients receiving constant infusion rhIL-2, at the described dose and schedule.