The aim of this study was to compare the effect on beta2-microglobulin (beta2-M) plasma levels of dialyzers with 3 low-flux synthetic membranes and regenerated cellulose (Cuprophan) in 12 chronic dialysis patients. The synthetic membrane materials chosen were low-flux polymethylmethacrylate (PMMA), low-flux polysulfone (PS 400), and polycarbonate-polyether (Gambrane). Adequate and comparable removal of small solutes was provided by dialyzers with all 4 membrane materials used under similar conditions. A significant reduction of beta2-M plasma levels was seen only with Gambrane while the other 2 synthetic membrane materials gave rise to increases similar to those known to occur with Cuprophan. After correction for the hemoconcentration caused by ultrafiltration, dialysis with Gambrane showed a 24% lower plasma beta2-M level while the beta2-M concentrations with the other 3 membrane materials were practically unchanged. In addition, the efficiency of Gambrane dialyzers in beta2-M removal was able to significantly lower the predialysis plasma beta2-M levels after only 5 dialysis sessions. The hemocompatibility of the 3 synthetic low-flux membranes as judged by the white blood cell (WBC) count and complement activation was similar and therefore cannot be used to explain the different beta2-M plasma levels. In anticipation of gaining further insight into the mechanisms of accumulation and deposition of beta2-M in dialysis patients, a worthwhile approach may be to use a low-flux membrane such as Gambrane which combines removal with protection against potential activating factors in the dialysis fluid.