Prostaglandins of the E-type are potent ductus dilatators not only in vitro but also in vivo, as could be shown in the former literature. We report on 20 newborn children, in whom we only used prostaglandin E2 to perform a better lung or kidney perfusion by opening the ductus arteriosus. The diagnoses of the children were: pulmonary atresia + ventricular septal defect +/- transposition of the aorta, tricuspid atresia, hypoplastic left heart syndrome, transposition of the great arteries +/- ventricular septal defect, coarctation of the aorta and tetralogy of Fallot. The dosis pattern of the prostaglandin E2 infusion was in 17 patients the same, starting with 0.1 microgram/kg body weight/min and consecutive reduction depending on the capillary pO2, in the last 3 patients we started with 0.05 microgram/kg body weight/min. In 7 patients we gave an oral preparation of prostaglandin E2 intermittently. The duration of treatment was between 15 min and 37 days. There was a significant increase of the capillary pO2 under prostaglandin E2 treatment (p less than 0.0001), the increase of capillary pO2 correlates negatively with the initial pO2 before treatment (p less than 0.05), but there is no dependence on the age of the children. The side effects of this therapy are discussed, especially the dangerous apnoic spells.