The effect of changing pulmonary artery pressure during flushing(flushing pressure) on lung preservation was examined in an ex vivo rabbit lung perfusion model. Both lungs were flushed in situ with 200 ml of a preservation solution (extracellular fluid [ECF] type) at 8°C, at a constant flushing pressure maintained by regulating the flushing flow rate from 20 to 120 ml/min. In the controls, the flushing pressure was maintained at 15 mmHg and the lungs were assessed without storage. In the other 5 groups(n=7 in each group), the lungs were flushed at pressures of 5, 10, 15, 20, and 25 mmHg, respectively. The heart-lung block was then harvested, and immersed in the same solution at 8°C for 24 hr. After 24 hr of storage, the block was reperfused with pooled venous blood for 10 min, and then with oxygenated blood for another 60 min in a closed circuit. Assessment of lung function included blood gas analysis of effluent blood, pulmonary artery pressure, airway pressure, wet:dry weight ratio, and histologic study.At flushing pressures of 5, 20, and 25 mmHg, uniform and clear flushing out of the pulmonary vascular beds was not obtained, resulting in postperfusion pulmonary hypofunction and a high incidence of pulmonary edema. However, at flushing pressures of 10-15 mmHg, we succeeded in completely flushing out the pulmonary vascular beds, and managed to preserve good pulmonary function. In conclusion, we determined the optimal flushing pressure for rabbit lung preservation to be 10-15 mmHg.