Elimination characteristics of beta 2-microglobulin (BMG) during hemofiltration (HF) with acrylonitrile (AN69) and polysulfone (PS) hemofilters were investigated in a prospective clinical investigation. Seven chronic uremics on regular HF were treated for 4 weeks, three times a week, with AN69 hemofilters. The study was then repeated with PS hemofilters. There were no significant differences in the patients' body weight, the ultrafiltrate volume per session, and the duration of each HF session between both treatments. At the start of HF, arterial plasma concentration of BMG was (for AN69) 33.5 +/- 4.0 mg/L (mean +/- SD) and (for PS) 35.8 +/- 6.5 mg/L (NS); at the end of HF it was (for AN69) 11.0 +/- 1.8 mg/L and (for PS) 17.5 +/- 4.2 mg/L (p less than 0.001). The amount of BMG in total ultrafiltrate was (for AN69) 179.3 +/- 22.6 mg and (for PS) 140.6 +/- 26.8 mg (p less than 0.02). With AN69 hemofilter, maximum BMG plasma clearance and sieving coefficient were 51.0 +/- 9.5 mL/min and 0.42 +/- 0.04 at 60 minutes. With PS hemofilter, maximum BMG plasma clearance and sieving coefficient were 37.4 +/- 5.7 mL/min and 0.27 +/- 0.03 at 15 minutes. Twenty-two percents of BMG entering the AN69 hemofilter at 15 minutes were adsorbed on the membrane (p less than 0.001). BMG elimination with the AN69 hemofilter was more efficient than with the PS hemofilter. Long-term studies will be necessary to demonstrate whether this difference is of any clinical significance.