The effects of kaolin-pectin suspension and of activated charcoal on aspirin absorption were compared. Ten fasting volunteers each received on five separate occasions three 325-mg aspirin tablets with: (1) 240 ml of water, (2) 10 g of activated charcoal in a slurry with 240 ml of water, (3) 30 ml of kaolin-pectin suspension with 210 ml of water, (4) 60 ml of kaolin-pectin with 180 ml of water, and (5) 90 ml of kaolin-pectin with 150 ml of water. Aspirin bioavailability was estimated from spectrophotometric assay of total 48-hour urinary salicylate recovery. The mean urine salicylate recovery following administration of activated charcoal (69.5%) was significantly less (p less than 0.01) than that following administration of 30, 60 or 90 ml of kaolin-pectin (90.6, 94.6 and 95.3%, respectively) or of water only (98.6%). The mean percent aspirin recoveries for the 30-ml and 60-ml kaolin-pectin treatments were significantly less than that for water only (p less than 0.05). Neither activated charcoal nor kaolin-pectin delayed the rate of aspirin absorption. Although kaolin-pectin reduces the absorption of aspirin, the effect would be of marginal clinical importance. Kaolin-pectin suspension is not recommended as a treatment for aspirin poisoning.