This study examines the extent of endothelial damage following a period of irrigation with various crystalloid irrigation fluds. Both arteries and veins were evaluated after irrigation with normal saline, lactated Ringer's. balanced salt solution (BSS), and balanced salt solution plus(BSS⁺). The arterial and venous endothelia were examined with the scanning electron microscope. Using a randomized blind observer scoring system. micrographs were evaluated for changes in nuclear shape, cell junction integrity, cytoplasm changes, and sloughing of the endothelial cell layer. BSS⁺ and BSS produced stastically significant(p<.001) improvement over the other two irrigation fluids in the arteries. BSS⁺ and BSS were stastically superior(P<.00l) in the venous vessels. The compositions of BSS and BSS⁺ tend to maintain a physiologic environment in the presence of ischemia. These maintained a morphologic appearance closer to that of perfusion-fixed controls The data suggest a protective effect of such physiologic preparations on the endothelium. The preservation of intact endothelium may play a role in decreased platelet activation. continued production of prostacyclin, and maintenance of and intact barrier between the intra-cellular and extracellular spaces. This could enhance the survival of transplanted or transferred tissue, by helping to maintain nearly normal endothelium during surgery.