The expression of the adhesion molecules LFA-1 (CD 1 la-CD 18), Mac-1 (CDlib-CD 18), and LAM-1 on predialysis and intradialysis neutrophils (PMN) was analyzed by flow cytometry in 10 chronic hemodialysis patients (CHD) and compared with age-matched normal controls. All patients were dialyzed either with a polyacrylonitrile, or a polysulfone membrane. To appreciate the influence of the interdialytic time, we compared the samples of Monday (3 days without dialysis), with those of Wednesday (2 days without dialysis). A patient group not treated with recombinant human erythropoietin (rHuEPO) was also included to analyze the influence of r-HuEPO. We found on the predialysis and intradialysis samples that the expression of CD11a as not different in the CHD patients and in the normal controls. Hemodialysis was associated with a rapid and significant reduction in LAM-1 on the 15- and 30-min samples (p < 0.05). This reduction was only transient, and returned to near predialysis levels after 120 min dialysis. The MAC-1 increased significantly after 30 min dialysis (p < 0.1), and remained at the end of the dialysis procedure still substantially above the predialysis levels (p < 0.01). On the other hand, we have found a significant (p < 0.005) up-regulating of the MAC-1, and a down-regulating of the LAM-1 in the predialysis samples. We noticed further a significantly lower expression (82 ± 9.6%) for LAM-1 in these predialysis samples (p < 0.005). These results demonstrate that ‘high MAC-1 low LAM-1’eutrophils were not only a dialysis-related phenomenon, but that they were already present before the hemodialysis session, nor was there any difference between the interdialytic times or compared with the r-HuEPO treat