Interleukin-2, a lymphocyte product, has well demonstrated antitumor activity in humans. Early clinical studies showed hemodynamic alterations in patients receiving the drug as antitumor immunotherapy. We serially assessed interleukin-2-associated hemodynamic parameters and left ventricular ejection fractions in five patients with neoplastic diseases unresponsive to conventional therapies. By day 4 of therapy, compared with baseline (preinterleukin-2), all patients developed tachycardia (p less than 0.01), decreased mean arterial blood pressure (p less than 0.05), increased cardiac index (p less than 0.05), and decreased systemic vascular resistance (p less than 0.01). In addition, left ventricular ejection fraction fell from 58.0 +/- 4.7 to 36.4 +/- 4.0 percent (0.05 less than p less than 0.10), which was associated with a trend toward left ventricular dilatation manifested by an increase in left ventricular end-diastolic volume index. Transient renal dysfunction was noted in all five patients, and one developed transient respiratory failure; both types of organ dysfunction recovered to baseline values after cessation of immunotherapy. Thus, interleukin-2 induces multiple reversible cardiovascular abnormalities that are similar to the hemodynamic manifestations of human septic shock.