It has been reported that activated charcoal reduces intestinal gas production after ingestion of beans as evidenced by decreased breath hydrogen excretion and decreased passage of flatus. In the present study we assessed the ability of activated charcoal to reduce intestinal gas production by in vitro and in vivo methods. In vitro studies were performed using human fecal homogenates incubated with or without additional carbohydrate. In all studies hydrogen and carbon dioxide production and consumption occurred at similar rates in the charcoal-treated homogenate as compared with the untreated control. The influence of activated charcoal on gas production, in vivo, was studied by double-blind assessment of breath hydrogen excretion and flatus excretion after ingestion of a baked bean meal. No significant difference was observed in breath hydrogen concentration or number of passages of flatus in subjects who ingested 16 capsules of activated charcoal (4 g) as opposed to the placebo. We conclude that activated charcoal does not influence gas formation in vitro or in vivo.