To examine the effect of preoperative prostaglandin infusion on surgical mortality the records of all patients aged less than or equal to 28 days operated between January 1979 and December 1981 for obstructive lesions of the systemic circulation were reviewed. Forty patients had coarctation of the aorta, five interrupted aortic arch, and seven critical aortic stenosis. Fourteen patients received intravenous prostaglandin before operation. Among preoperative variables low cardiac output was identified as a possible risk factor for hospital death, whereas the presence of a raised blood urea concentration was possibly significantly associated with hospital mortality only in patients not treated with prostaglandin. The preoperative administration of prostaglandin had a strongly favourable influence: 11 out of 38 (29.0%) patients who did not receive prostaglandin died compared with none of 14 treated with prostaglandin. The two groups were otherwise comparable with respect to the incidence of coagulopathy, urgency of operation, associated anomalies, and other medical treatment. Mean age at operation was younger and mean admission blood urea concentration higher in the group treated with prostaglandin, whereas the incidence of preoperative low cardiac output was probably higher. It is concluded that short term preoperative infusion of prostaglandin in associated with a significant reduction in early surgical mortality in this high risk group of infants.