Intercellular adhesion molecule-1 (ICAM-1) is expressed on the surface of various types of cells, including lymphocytes, monocytes and vascular endothelial cells. Recently, ICAM-1 was reported to be shed from the cell membranes and released into circulation. The soluble ICAM-1 (sICAM-1) level has been reported to be increased in patients with certain inflammatory diseases. It is well known that the functions of leukocytes including neutrophils, lymphocytes and monocytes are impaired in patients with chronic hemodialysis. In this study, we evaluated the effect of hemodialysis (HD) on the lymphocytes and monocytes by periodically measuring the serum concentration of sICAM-1 during HD. Pre-HD sICAM-1 levels in chronic hemodialysis patients were significantly increased as compared with healthy subjects. Two hundred and forty minutes after the start of HD, sICAM-1 levels were significantly higher than the pre-HD levels. The sICAM-1 levels at the venous side of the dialyzer were significantly increased compared with the levels at the arterial side. There was no significant difference between the sICAM-1 levels of the patients under hemodialysis with the regenerated cellulose membrane and those with the polymethylmethacrylate membrane. These results suggest that ICAM-1 is shed from the surface of mononuclear cells (lymphocytes and monocytes) and released into circulation stimulated by hemodialysis membranes. Chronic hemodialysis may impair the function of mononuclear cells by inducing the shedding of ICAM-1.