The peracetic acid-based sterilant Renalin® is increasingly being used for reprocessing hemodialyzers. In order to evaluate the effects of reprocessing on (32-microglobulin (β2M) kinetics and complement activation in chronic hemodialysis patients, we compared 4 dialyzer membranes on 1st, 2nd and 4th use of the membrane. Dialysis with new cuprammonium rayon dialyzers (0.8 m2) for 4 h resulted in a nonsignificant increase in serum β2M concentrations of 10.7% (corrected for changes in extracellular volume) and significant generation of the complement component C3a des Arg. On reuse, minimal changes in serum β2M levels were noted and complement activation was absent. Dialysis with new cellulose acetate (CA, 1.5 m2), polyacrylonitrile (AN69 HF, 1.6 m2) or polymethylmethacrylate (PMMA, 1.6 m2) membranes resulted in significant decreases in serum β2M levels (19.5, 31.7 and 50.8%, respectively). Reprocessing had negligible effects on the removal of β2M by CA and AN69, but by the 4th use halved the effectiveness of PMMA. Reprocessing reduced the significant generation of C3a des Arg observed with new CA and PMMA membranes. We conclude that, except for PMMA, Renalin reprocessing has minor effects on the ability of the membranes to remove β2M and improves the biocompatibility of all membranes s