1 Fifty infusions of epoprostenol (PGI2) were made, usually increasing the infusion rate until adverse effects were encountered. The volunteers were appraised that they might experience headache and facial flushing. 2 Facial flushing, headache, tachycardia and decrease in diastolic blood pressure were seen in almost all subjects. Erythema over the venous infusing site was also encountered in 13 infusions. Less common effects were sudden bradycardia, pallor and sweating--the vagal reflex--(seven times) and chest pain (twice). Other complaints included restlessness, abdominal discomfort, nausea and drowsiness. 3 The literature on side effects reported during PGI2 infusion is reviewed and recommendations are made concerning administration of PGI2.