It was reported that ethanol–induced bronchoconstriction was associated with elevated serum levels of aectaldehyde and histamine in Japanese asthmatic patients, but there is no study to investigate the airway response to acetaldehyde. We performed this animal study to test the hypothesis that acctaldehyde has the bronchospastic action via histamine release. First, we investigated the airway response to ascending doses (31.3, 62.5, 125. and 250 MM) of inhaled ethanol or acctaldehyde in guinea–pigs. Secondly, guinea–pigs pretreated with intraperitoneal injection of saline or 20 mg/kg diphenhydramine inhaled acetaldehyde. Finally, guinea–pigs pretreated with intraperitoneal injection of saline or 0–5 mg/kg atropine sulfate inhaled acetaldehyde. Inhalation of acetaldehyde. but not ethanol, caused bronchoconstriction in a dose–dependent manner. The bronchoconstriction induced by inhaled acetaldehyde was completely prevented by pretreatment with diphenhydramine. Atropine had no preventing effect against the acetaldehyde–induced bronchoconstriction. In conclusion, acetaldehyde has the bronchospastic action via histamine release in guinea–pigs. It is suggested that histamine HI–antagonists may be available for preventing alochol–induced asthma.