During hemodialysis, platelets are activated and release alpha-granule-specific proteins. GMP-140 is a glycoprotein stored in the alpha-granules of platelets, which is selectively expressed on the plasma membrane of activated platelets. Using a specific monoclonal antibody against this protein (CD 62), we have evaluated the influence of different dialysis membranes on hemodialysis-induced platelet activation in vivo by flow cytometry in nine patients with end-stage renal disease on maintenance hemodialysis. Five membranes were evaluated: Cuprophane, cellulose acetate, polymethylmethacrylate, polysulphone and polyacrylonitrile (AN-69). Blood samples were obtained before hemodialysis and from the inlet and outlet lines five minutes after the beginning of hemodialysis. A significant increase in the GMP-140 expression was observed in samples obtained from the outlet line compared with samples obtained from the inlet line for all membranes evaluated, but the extent of this increase depended on the type of membrane used: Cuprophane 13.95 +/- 3.94%, cellulose acetate 7.4 +/- 4.52%, polymethylmethacrylate 6.93 +/- 4.6%, polysulphone 3.83 +/- 2%, and AN-69 2.14 +/- 2.19% (mean +/- SD). Cuprophane induced the highest degree of platelet activation (P < 0.05). Cellulose acetate and polymethylmethacrylate induced more platelet activation than polysulphone or AN-69 (P < 0.05). These data demonstrate that all hemodialysis membranes induce platelet activation but to a variable extent, cuprophane being the most activating membrane, cellulose acetate and polymethylmethacrylate showing an intermediate potential of activation, while the more biocompatible membranes, polysulphone and AN-69, inducing the lowest degree of platelet activation.