Background/Aim: CD31 on leukocytes is the adhesion molecule involved in the leukocyte extravasation in inflammatory conditions. During hemodialysis with cellulosic membranes, it is considered that activated leukocytes adhere to endothelium, but do not show extravasation. However, it is not elucidated why activated leukocytes do not show endothelial transmigration during hemodialysis with cellulosic membranes. Methods: In the present study, changes in the expressions of Mac-1 and CD31 on granulocytes and monocytes were analyzed by flow cytometry during hemodialysis in 7 patients treated with regenerated-cellulose (RC) membranes and next with polysulfone (PS) membranes. Results: During dialysis with RC, Mac-1 expressions on granulocytes and monocytes both significantly increased as compared with predialysis values and across the dialyzer. During dialysis with RC, the CD31 expression on granulocytes and monocytes significantly decreased as compared with predialysis values. During dialysis with PS, changes in Mac-1 and CD31 expressions on granulocytes and monocytes were smaller than those during dialysis with RC. Conclusions: Decreased CD31 expression on leukocytes may affect leukocyte function more in patients chronically hemodialyzed with RC than in those hemodialyzed with PS, since CD31 is important in leukocyte transendothelial migration in inflammatory conditions.