The molecular adsorbent recycling system (MARS) represents a cell-free, extracorporeal, liver assistance method for the removal of both albumin-bound and water-soluble endogenous toxins. The aim of the present study was to evaluate the short- and long-term removal capacity and selectivity of the different inbuilt dialysers and adsorption columns (uncoated charcoal, anion exchanger resin). Levels of endogenous toxins and parameters of hepatic synthesis and necrosis were therefore monitored before, during and after the MARS treatment phase in 10 patients. Moreover, blood and dialysate clearances of urea, creatinine, bilirubin and bile acids were determined during a single treatment. The significant increasing time course of total bilirubin blood levels before the start of the treatment could be stopped and reversed in a significant decreasing time course. The removal rates of urea nitrogen, bilirubin and bile acids during a single treatment amounted to 55.5 +/- 4.0, 28.3 +/- 3.9, and 55.4 +/- 4.0% (mean +/- SEM), respectively. The efficacy of removal of albumin-bound toxins sharply declined early after initiation of the treatment to become negligible after 6 h. In conclusion, both albumin-bound and water-soluble toxins are adequately removed by the MARS. Our data suggest that the rate and efficacy of removal of albumin-bound toxins are related to both the strength of the albumin binding and the saturation of the adsorption columns.