The administration of high-dose continuous intravenous infusion interleukin-2 (IL-2) is able to induce the presence of lymphokine-activated killer (LAK) cells. LAK are able to nonspecifically lyse tumor cells. They are also able to lyse endothelial cells, which accounts for, at least in part, the capillary leak syndrome seen as one of the toxicities with this therapy. A pulmonary manifestation of capillary leak syndrome is the presence of pulmonary edema. We postulated that capillary leak may also be a mechanism by which LAK could conceivably reach pulmonary metastases or could be a reflection of damage of endothelial cells in vasculature supplying metastases and that capillary leak syndrome may actually correlate with the response of pulmonary metastases. We examined our database of patients with lung metastases treated with high-dose continuous infusion IL-2 (18 MIU/m(2)/day for 3 days) regimens. Eighteen patients had the following characteristics: melanoma (11), renal cancer (7), median age of 67 years (range, 28-79 years), and males (15). All patients were treated by oncology nurses on either the stem cell transplant unit or oncology ward. Pulmonary edema was defined as the presence of pleural fluid on a chest X-ray, computed tomography (CT) scan, and/or as noted on a physical examination by at least 2 observers. No patients required endotracheal intubation, mechanical ventilation, or an intensive care unit transfer. The median number of cycles received was 6 (range, 1-13). All 8 responding patients (6 patients with melanoma, 2 patients with kidney cancer) manifested pulmonary edema during interleukin-2 therapy. Four patients with pulmonary edema were nonresponders. The presence of pulmonary edema correlated with the response to therapy (p = 0.01). The median duration of response of pulmonary nodules was 5 months (range, 1-16 months). There is a correlation between the development of pulmonary edema and the response of pulmonary metastases in patients with melanoma and kidney cancer treated with high-dose continuous infusion interleukin-2.