The purpose of this study was to examine the effects of a small dose of prostaglandin E1 on systemic and cerebral oxygenation. Thirty patients for coronary artery bypass graft surgery were randomly divided into two groups: Group 1 received PGE1 25 ng.kg-1.min-1. Group 2 received PGE1 50 ng.kg-1.min-1. After measuring baseline hemodynamics and mixed (SvO2) and juglar (SjvO2) venous oxygen saturations, administration of PGE1 at a rate of 25 ng.kg-1.min-1 or 50 ng.kg-1.min-1 was started before and during CPB. In group 2, mean arterial pressure (MAP) decreased during CPB, while in group 1, MAP was unchanged during CPB. There was no change in SjvO2 both in group 1 and group 2 before and during CPB. The administration of PGE1 at a rate of 25 ng.kg-1.min-1 during CPB was suitable for the maintenance of SvO2 and SjvO2.