To test the effects of alprostadil on pulmonary dysfunction after caediac operations, we studied 24 male patients undergoing; aortocoronary bypass. Twelve were given an intravenous infusion of alprostadil (synthetic prostaglandin E 1), 20 ng · kg −1 · min −1, in a double-blind manner during operation; the other 12 were controls. Duration of artificial respirator use and frequent blood gas analyses were used to assess postoperative pulmonary function. Use of the artificial respirator postoperatively was significantly lower in the prostaglandin group (mean time, 5.25 ± 1.81 hours) compared with the controls (mean time, 8.34 ± 4.35 hours) ( p = 0.047). The proportion of patients with hypercapnia and with hypoxia determined every 4 hours for the first 24 hours after extubation was significantly lower in the prostaglandin group compared with the controls ( p < 0.0001). These results indicate that synthetic prostaglandin E 1 may play a role in protecting lung tissue during extracorporeal circulation.