Ciprofloxacin is a broad-spectrum antibiotic orally active against both gram-positive and gram-negative bacteria. Recent literature indicates that orally administered activated charcoal can alter the bioavailability of many drugs and in vitro studies have demonstrated an interaction with ciprofloxacin. To evaluate in vivo the effects of activated charcoal on ciprofloxacin pharmacokinetics, six healthy volunteers received, according to a cross-over design, either ciprofloxacin 500 mg alone or concomitantly 1 g activated charcoal. The coadministration of the latter drug did not influence any of the considered pharmacokinetic parameters. Activated charcoal at a clinically effective dose, therapeutically used in gaseousness, does not alter ciprofloxacin pharmacokinetics.