The chest roentgenograms of 54 patients receiving high dose interleukin-2 with or without lymphokine-activated killer cell therapy for advanced cancer were retrospectively reviewed. Thirty-nine patients (72 percent) developed chest roentgenographic abnormalities consisting of pleural effusions, 28 (52 percent); diffuse infiltrates (pulmonary edema), 22 (41 percent); and focal infiltrates, 12 (22 percent). These abnormalities resolved in 30 of 39 (77 percent) patients by four weeks after therapy. Simple pleural effusions were the only residual roentgenographic abnormalities seen and were present primarily in patients receiving IL-2 by bolus intravenous injection (8 of 28) (29 percent) as compared to continuous intravenous infusion (1 of 24) (4 percent) (p = 0.03). Only roentgenographic evidence of pulmonary edema appeared to correlate with the degree of clinical pulmonary toxicity (p = 0.001). The development of chest roentgenographic abnormalities correlated with the administration of IL-2 solely by bolus intravenous injection (p = 0.04), a pretreatment FEV1 of less than 3 L (p = 0.04), and treatment associated bacteremia (p = 0.09), but not with prior therapy, the presence of pulmonary metastases or the degree of systemic capillary leak as measured by percentage of weight gain during therapy. Although the roentgenographic abnormalities did not relate to the number of LAK cells received, two patients developed sudden onset of dyspnea and chest roentgenographic evidence of pulmonary edema shortly after the first LAK cell administration, implying that a direct cause-and-effect relationship exists in some patients. Possible mechanisms for these IL-2 related chest roentgenographic abnormalities and pulmonary toxicity in general are discussed.