The addition of prostaglandin to the single-flush technique of lung preservation is considered to enhance subsequent graft function. We have evaluated the use of the prostacyclin analog, Iloprost, in an animal model of unilateral lung transplantation. Group 1 (n = 5) received Iloprost as a pretreatment intravenously (20 ng/kg/min) and as an additive (20ng/L) to 20 ml/kg of modified Euro-Collins solution. Group 2 (n = 5) received no Iloprost, either as pretreatment or added to the perfusate. Perfusate distribution within the lungs during flush perfusion was assessed using99mTc-labeled microaggregates of albumin. After the initial preservation technique the lungs in both groups were stored for 6 hr in Euro-Collins solution at 4°C. Thereafter, left lung transplantation was followed by ligation of the contralateral pulmonary artery and bronchus, rendering the animal completely dependent on the transplanted, stored lung. Preservation was assessed by animal survival, measurement of hemodynamic and blood gas data for 24 hr at a fixed FiO2 (0.4) and tidal volume (10 ml/kg), and at sacrifice by measurement of transplanted lung water. By these criteria, both group 1 and 2 lungs were well preserved. The addition of Iloprost to group 1 animals appeared to confer no measurable benefit in terms of lung cooling, perfusate distribution, postoperative graft function, or total lung water.