Prostaglandin E1(PGE1) was administered to 27 infants in whom pulmonary or systemic blood flow was entirely or significantly dependent upon the patency of the ductus arteriosus. In 12 patients with pulmonary atresia or severe pulmonary stenosis, PGE1 infusion was followed by an improvement in hypoxemia and acidemia (group I). In 2 patients with left ventricular outflow-tract obstruction, PGE1 infusion was followed by an improvement in arterial blood pressure, peripheral perfusion and urine output (group II). In 5 patients with d-transposition of the great arteries and intact ventricular septum who had persistent severe hypoxemia after creation of an interatrial communication, PGE1 infusion improved the arterial oxygenation with dilatation of the ductus arteriosus (group III). Seven patients (3 of group I, 2 of group II and 2 of group III) failed to respond to PGE1. There were no fatal side effects. It is concluded that PGE1 therapy is highly effective in stabilizing pre-operative conditions of infants with ductus-dependent congenital heaat disease. prostaglandin E1 i ductus-dependent congenital heart disease ; pre-operative management Adequate pulmonary or systemic blood flow is dependent upon the patency of the ductus arteriosus in some of the critically ill infants with congenital heart disease. Partial or complete closure of the ductus after birth results in hypoxemia or severe heart failure with the progressive development of acidemia. Although palliative or corrective surgical procedures were available, mortality in these infants was high, because of their deteriorated pre-operative conditions and of the difficulties of the surgical techniques. Elliott et al. (1975) and Olley et al. (19Th, 1976) reported that administration of prostaglandins E1 (POE1) and E2 (PGE2) to such infants improved the deteriorated conditions. Following their reports, several authors have recongn-