A rise in blood acetaldehyde concentrations following alcohol ingestion was significantly inhibited when healthy nonflushing subjects were administered a clinical dose of pantethine orally. However, similar findings were not observed in flushing (alcohol-sensitive) subjects lacking hepatic low Km aldehyde dehydrogenase (ALDH). The blood ethanol concentrations were not altered by this treatment in either flushing or nonflushing subjects. Acetaldehyde (45 microM) added in vitro to whole blood and plasma obtained 1 hr after pantethine administration disappeared as the incubation continued similarly as with blood and plasma obtained prior to pantethine treatment. Pantethine-related metabolites, such as taurine, pantetheine, coenzyme A, and pantothenate, activated ALDH in vitro. Hepatic acetaldehyde levels following ethanol loading of rats treated with pantethine were much lower than in untreated rats. The pantethine action observed only in nonflushing subjects might be due to an accelerated oxidation of acetaldehyde by the activation of low Km ALDH by pantethine-related metabolites formed in the liver.