Comparative flow cytometric measurement was used to evaluate the significance of leukocyte adhesion molecule (LAM) activity changes during hemodialysis (HD) with different cellulosic and non cellulosic membranes. Six hemodialysis patients (men) who were in a maintenance program for more than 6 months were treated consecutively with five different dialyzers (cuprophan, hemophan, 2 types of cellulose acetate, and polysulfone). During each study HD, blood was sampled from the arterial line at 0, 15, and 60 min and from the venous port at 3 min to harvest leukocytes immediately after the first cell-membrane contact. After whole blood lysis preparation, leukocytes were incubated with fluorescent antibodies to label LAM CD 11A/18 (LFA-1), CD 11B/18 (Mac-1), CD 11C/18 (p150/95), and CD 54 (ICAM-1) (Becton-Dickinson, San Jose, CA). Data were acquired for the granulocyte, monocyte, and lymphocyte population based on forward and 90 degrees scatter light measurements. Accuracy of gating was verified by CD 14/45 staining for all samples. Baseline integrin expression for the selected populations before biomaterial contact was found to be heterogeneous for different patients, but underwent changes for the same patient during HD treatment. The fluorescent intensity corresponding to specific integrins was characterized by different patterns of up/down regulation with maximal deviations occurring at 3 min. Fluorescent intensity of the granulocyte and monocyte populations sampled at 15 min was 40-50% lower as compared with those sampled immediately after the first biomaterial contact. Based on the basal fluorescence levels and values recorded after the first biomaterial contact and those at 15 min, two coefficients were generated to compare membrane properties.