Plasma aromatic amino acid (AAA) and branched-chain amino acid (BCAA) concentrations were determined in 197 alcoholics. The BCAA/AAA molar ratio in patients with alcohol withdrawal symptoms was compared with the ratio in patients without such symptoms. The BCAA/AAA molar ratio in patients with emotional disturbance or with transient hallucination was significantly lower than that in patients without these symptoms. The BCAA/AAA molar ratio tended to be lower in patients with alcohol withdrawal convulsion or with delirium tremens as compared to patients without such symptoms. The BCAA/AAA molar ratio had a negative correlation with plasma total bilirubin and LDH and had a positive correlation with plasma choline esterase and albumin. Oral administration of amino acid preparations (Aminoleban EN) to the patients elevated the BCAA/AAA molar ratio and normalized liver function. These results indicate that abnormalities of amino acid metabolism caused by liver damage in alcohol dependence may have an important role in the pathogenesis of alcohol withdrawal syndrome.