BACKGROUND Plasma concentration of beta2-microglobulin (beta2-m) in the case of renal insufficiency is about 20 to 30 times higher than normal. Beta2-m is associated with secondary amyloidosis, a late complication of regular dialysis therapy. To prevent the complications of secondary amyloidosis beta2-m should therefore be eliminated as efficiently as possible during dialysis treatment. This can be accomplished with dialysis membranes which guarantee sufficient clearance for this molecule. It is a matter of discussion whether removal of beta2-m by dialysis may be able to prevent secondary amyloidosis. METHODS The dialyzers Diacap HI PS 15 (B. Braun Melsungen) and F70 S (Fresenius Medical Care) were compared in five anuric dialysis patients. Arterial blood was taken at the start and at the end of dialysis. Dialysate samples were taken after 30 and 210 minutes and filtrate samples after 60 and 240 minutes from the start of dialysis. Beta2-m and total protein concentration were measured in plasma, filtrate and dialysate. SDS-PAGE of proteins in the filtrate was carried out and kinetics of beta2-m (Kt/V(beta2-m)) were calculated using the Stiller/Mann model. RESULTS In both dialyzers beta2-m is detectable at any time in the dialysate leaving the dialyzer. In the filtrate beta2-m concentration is about 10 times higher than in the dialysate. Protein pattern in filtrate of both dialyzers is similar and corresponds to that of the glomerulum filtrate. Beta2-m reduction ratio is slightly lower than urea reduction ratio. Using both dialyzers Kt/V(beta2-m) was 0.80, removing about 60% of the generated beta2-m. CONCLUSIONS In both dialyzers there is considerable removal of beta2-m. Examination of beta2-m kinetics showed an optimum of Kt/V(beta2) of 0.80 which can not be surpassed. Only 60% of generated beta2-m can be removed by three times per week hemodialysis therapy using high-flux dialyzers.