It is known that prostaglandin E1 (PGE1) is a potent vasodilator and improves red cell deformability. Single lung-ventilation sometimes occurs under lung transplantation, lung cancer surgery and traumatic pneumonectomy, and may result in increased pulmonary resistance, right heart failure and severe hypoxemia. The present experimental study was undertaken to examine the effects of PGE1 on these states induced by single-lung ventilation and hypoventilation. Fourteen pigs weighing 32-33 kg were anesthetized, intubated and ventilated using a respirator and then randomly assigned to two groups, the control group and the PGE1 treated group, 7 pigs each. After median sternotomy to induce severe hypoxemia hypoventilation was induced and then the right hilus pulmonis was cross clamped. Mean blood pressure, mean pulmonary arterial pressure (PAP), pulmonary vessel resistance (PVR), right ventricular stroke work (RVSW) and arterial blood gases (PaO2 and SatO2) were measured at baseline, in the hypoventilation state, and 15 min, 1 hour, and 2 hours after the right hilus pulmonis clamping with hypoventilation. PGE1 (250 microg/20 ml saline) was administered via the central vein starting 15 min after right hilus cross clamping for 1 hour and 45 min in the PGE1 group. PGE1 significantly reduced PAP and PVR, normalized RVSW, and improved PaO2. PGE1 may be useful for the condition of increased pulmonary hypertension during single-lung ventilation and hypoventilation.