Background. This study compares the effect of lung preservation using flush perfusion of Euro-Collins or University of Wisconsin solution on the pulmonary vascular function of endothelium-dependent and endothelium- independent relaxations. Methods. Rings of canine intrapulmonary arteries were studied after 6 hours of cold ischemia in Euro-Collins or University of Wisconsin preservation solution. Endothelium-dependent and endothelium- independent relaxations were induced in organ chamber experiments. To also study pulmonary resistance vessels, endothelium-dependent relaxations were induced in in vitro perfused intact rabbit lungs. Results. In the organ chamber experiments, a moderate but significant (p < 0.05) reduction in endothelium dependent relaxations were found in the perfused and stored vessels. In perfused rabbit lungs, a decrease in the endothelial response occurred immediately after perfusion with Euro-Collins solution. However, a recovery and overshooting response was found after preservation with either solution and 6 hours of cold ischemia. A significant increase in the sensitivity of smooth muscle cells to nitric oxide was shown in both preparations. Conclusions. Both crystalloid perfusion fluids cause a decrease in endothelial function during the perfusion procedure. In contrast, endothelial function is well preserved during the ischemic time. University of Wisconsin solution induced a higher sensitivity of the vascular smooth muscle to the endothelium-derived relaxing factor nitric oxide. A reduction in pulmonary vascular resistance after University of Wisconsin preservation may be of importance in subsequent clinical lung transplantation.