1. The in-vitro binding of four drugs with differing physiochemical properties to two commercial charcoal preparations and two anionic binding resins was studied at 37 degrees C and pH 7.4. 2. The two charcoal preparations (Carbomix and Medicoal) behaved similarly and adsorbed metoclopramide and antipyrine to a greater degree than warfarin or paracetamol. 3. Cholestyramine had a significantly greater maximum adsorption capacity (K2) for warfarin and significantly lower adsorption capacity for paracetamol and metoclopramide than did the charcoals. 4. Colestipol behaved similarly but also bound metoclopramide to a significantly greater extent than did either cholestyramine or charcoal and antipyrine to a significantly lesser extent than did Carbomix. 5. There appeared to be no consistent relationship between the maximum adsorption capacity of the adsorbents for the drugs tested and the physicochemical properties of those drugs (e.g. basic or acidic structure, pKa or molecular weight).