A kindred with a familial hemoglobinopathy and familial primary pulmonary hypertension with autosomal dominant transmission has been identified. Affected family members were obvious from their cyanosis due to a reduced affinity for oxygen by the hemoglobin variant. The mother and one child had clinical pulmonary hypertension, whereas two siblings had cyanosis and preclinical pulmonary vascular disease as evidenced by abnormal perfusion lung scans and elevated levels of fibrinopeptide A in the face of normal pulmonary hemodynamics. In one, pulmonary hypertension could be induced with exercise. The studies on this family support the hypothesis that primary pulmonary hypertension may be initiated by abnormalities of the pulmonary vascular bed that predispose to in situ thrombosis. The possible common genetic transmission of the two diseases offers the speculation that the gene that confers predisposition to pulmonary hypertension may be located near the gene responsible for beta globulin.