Five patients with cardiopulmonary manifestations of Manson's schistosomiasis are described. Two patients had pulmonary hypertension, two had cyanosis and one had the very rare combination of both. The results of routine pulmonary function tests--not sufficiently studied in this form of schistosomiasis--are discussed in detail. Aside from a tendency to hyperventilate, found in all cases, the only significant abnormality encountered was hypoxemia due to increased right-to-left shunt in the cyanotic patients. Although more studies are needed, the results suggest that the pulmonary lesions are mainly vascular in nature. The pathogenesis of cyanosis in this disease is briefly discussed.