The properties of six adsorbents for Haemoperfusion were investigated in vitro: Amberlite XAD-2; Amberlite XAD-4; Haemocol; collodion coated charcoal; albumine-collodion encapsulated charcoal and activated carbon fibers. Carbromal and diazepam are most quickly removed from aqueous solutions by Amberlite XAD-2 and XAD-4. Of the charcoal containing materials, Haemocol eliminates most rapidly carbromal and diazepam; while activated carbon fibers remove phenobarbital faster. When heparinized blood is perfused, a remarkable reduction in platelet count is observed. The drop is most pronounced with Amberlite XAD-2 and XAD-4, but even when using charcoal preparations the platelet depletion can reach 10% of the original number over 5 hours. Haemolysis is most pronounced with Amberlite XAD-2, XAD-4 and Haemocol. As the efficiency of the adsorbents towards the various drugs differ and as their adverse effects also vary, the decision for a particular material will have to be made according to the individual case.