Pulmonary and cardiac functions were investigated in 13 patients hospitalized with nephropathia epidemica, a European form of hemorrhagic fever with renal syndrome. As compared with reference values, the patients' diffusion capacity for carbon monoxide was decreased (P = .002) and pulmonary clearance of inhaled technetium-99m-labeled diethylenetriamine pentaacetic acid was increased (P = .002). In four of 11 patients, arterial blood gas analysis disclosed a reduction in partial pressure of O2 (< 10 kPa) and oxygen saturation (< 94%). In three of 13 patients, chest radiography revealed interstitial infiltrates or pleural effusions. Lung volumes and expiratory flow rates of the patients were not significantly changed. By electrocardiography and echocardiography, no significant cardiac dysfunction was demonstrable. The pulmonary dysfunction was best explained by an alveolocapillary lesion. The two hantavirus-caused clinical syndromes, hemorrhagic fever with renal syndrome and hantavirus pulmonary syndrome, may be pathophysiologically more similar than appears from the clinical presentations.