The present stduy was undertaken to investigate the possible effect of Puffer fish skin extract (Pf) on the heptic acetaldehyde metabolism . It was obsrved that PF markedly decreased the acetaldehyde levels in blood and liver. The activity of mitochondrial aldehyde dehydrogenase (Ald DH) increased by induction of acute intoxicatiion of alcohol (5 g/kg) was further increased through pretreatment with PF for 2 weeks. When PF was given to rat fed with 25% alcohol solution instead of water for 6 weeks. the activity of Ald DH in mitochondrial fraction decreased to about 28% compared with sucrose-treated group. But after pretreatemnt of PF, the activity was restored to the normal level. By the treatment with disulfiram (300 mg/kg, once a day for 3days) was restored to the control after the pretreatment with PF. And also mitochondrial Ald DH activity in vitro was not changed. All these observations suggest that reduction of acetaldehyde levels are partly due to increase activity of mitochondrial Ald DH. Therefore, the recovery from intoxication of acetaldehyde may be enhanced by treatment with PF.