Eight patients underwent IV bolus therapy with recombinant interleukin-2 (Cetus Corporation, Emeryville, CA) for treatment of metastatic melanoma or renal cell carcinoma. The patients were randomized to receive interleukin-2 alone or interleukin-2 in combination with lymphokine-activated killer cells. Radiographs showed pulmonary edema in five of the eight patients. The changes ranged from mild interstitial edema (two patients) to frank pulmonary edema (three patients). The edema generally resolved within 4 days after the termination of therapy (four patients), however, one patient developed edema and arrhythmias approximately 7 days after interleukin-2 therapy ended. Seven of the eight patients had either cardiac arrythmias or angina. The mechanisms that contribute to the pathogenesis of these cardiac complications with interleukin-2 therapy remain unclear. The development of pulmonary edema is thought to be caused by capillary leakage and cardiac pulmonary edema due to cardiac toxicity of the drug. The radiologic appearances of these types of pulmonary edema were indistinguishable from one another and from other causes of pulmonary edema. Our study shows that interleukin-2 can cause pulmonary edema, cardiac arrhythmias, and unstable angina. The severity of these conditions is unrelated to dose.