Persistent pulmonary hypertension of the newborn infant can be difficult to distinguish from other cardiopulmonary causes of cyanosis during the newborn period. Infants with PPHN have cyanosis, tachypnea, acidemia, normal pulmonary parenchymal markings on the chest radiography, and anatomically normal hearts. We have identified and treated 11 infants and have noted several signs and symptoms not previously emphasized. These are cineangiocardiographic evidence of atrioventricular valve insufficiency in association with systolic murmurs and slow ventricular emptying, apnea, hypocalcemia, only a small rise in abdominal aortic blood oxygen tension during breathing of 100% oxygen, and no response to continuous positive airway pressure. Right-to-left shunting through the patent ductus arteriosus was documented in nine infants: in all six of those in whom simultaneous temporal and abdominal aortic blood oxygen tension measurements were made; in three by means of cardiac catheterization. Ten infants survived after variable courses and treatments which makes it difficult to ascribe improvement to any one therapy. The distinct increase in blood oxygen tension with tolazoline HCl and curare in some instances is discussed.