1 The adsorptive capacities of two preparations of activated charcoal have been studied both in vitro and in vivo using aspirin as a test compound. 2 The in vitro adsorptive capacities of the charcoal preparations were 477 mg of acetylsalicylic acid/g effervescent charcoal ('Medicoal'); 359 mg/g untreated standard charcoal ('Norit-A') and 482 mg/g reheated charcoal ('Norit A'). 3 In vivo both charcoal preparations significantly reduced peak salicylate concentrations and salicylate availability, to a similar extent (analysis of variance P less than 0.001). 4 Both charcoal preparations have similar capacities for adsorbing aspirin both in vitro and in vivo.