The Free fatty acid [FFA] induced massive erythrocyte crenation has been reported in patients undergoing extracorporeal circulation[EGG], suggesting that the crenated cells impair microcirculatory flow and tissue oxygenation during and after the operation. Effect of albumin administration on erythrocyte crenation was examined in 24patients undergoing open heart surgery at the department of Thoracic and Cardiovascular Surgery in the Kyung Hee University Medical Center Between January, 1989 and August, 1989: 8 patients of 24 patients [group A] were given 50 gm albumin, another 8 patients of 24 patients [group B] were g en 26 gm of albumin and the other 8 patients of 24 patients [group C] were not given any albumin as a part of the priming solution. Erythrocyte crenation was almost completely prevented in the patients given 50 gm albumin. Crenated erythrocytes d urging ECC were 3.6* 0.4 % [meanulcornerD] of all erythrocytes and 3.1*0.6% after ECC. This was significantly lower than in patients without albumin administration [64.2*9.5% during ECC and 28.7*1.9% after ECC]. But the effect was less striking in the patients given 25 gm albumin, 37.8* 12.0 % during ECC and 27.8*3.9 % after ECC. Maintaining an adequate level of plasma albumin is important in preventing erythrocyte crenation during ECC, improving microcirculatory flow in patients undergoing open heart surgery.