1. The effect of activated charcoal on the absorption and elimination of astemizole and its metabolites was studied in healthy volunteers. 2. Subjects were divided into three groups containing seven subjects each. One group received 30 mg of astemizole with water only (control) and another group with 25 g of activated charcoal. The third group received multiple doses (12 g) of charcoal from 6 h onwards twice daily for 8 days. The concentrations of astemizole and its metabolites in plasma were measured by radioimmunoassay for 192 h. 3. Activated charcoal, administered immediately after astemizole ingestion, reduced the absorption of astemizole by 85% (P < 0.001). Multiple doses of activated charcoal, administered throughout the period of astemizole elimination, had no significant effect on the rate of elimination or the area under the curve from 0 to 192 h. 4. The absorption of astemizole from the gastrointestinal tract can be effectively prevented with activated charcoal. Because astemizole is rapidly absorbed, charcoal should be administered as soon as possible in acute astemizole poisoning. Multiple doses of charcoal do not seem to shorten the elimination half-life of astemizole.