Shifts in the visible spectrum of aqueous bilirubin (BR) resulting from the addition of soluble polyvinylpyrrolidone (PVP) suggest specific interactions. Hence, isotherms were determined for the adsorption of BR from aqueous solution onto solid, cross-linked PVP and onto cholestyramine (CA) (used as a reference adsorbent) at 0, 10, 20 and 25 degrees C. Although adsorption onto PVP reaches equilibrium values more rapidly than for CA, the latter adsorbent has a larger capacity. Furthermore the isotherms for PVP are independent of temperature while those for CA show an increase in BR adsorbed with an increase in temperature.