Metabolism of phenylalanine and tyrosine was impaired in chronic alcoholism as shown by an increase in concentration of phenylalanine and by a decrease in content of tyrosine in blood serum as well as by elevated urinary excretion of phenylalanine and phenylpyruvic acid and by decreased excretion of homogentisinic acid. Loading with L-phenylalanine made these impairments more distinct. The data obtained suggest that the activity of phenylalanine hydroxylase system from liver tissue is decreased in chronic alcoholism. The most distinct impairment in phenylalanine metabolism was observed in alcohol withdrawal syndrom. The decrease in the activity of phenylalanine hydroxylase system may cause an accumulation of phenylalanine and its metabolites in brain tissue at well as an impairment of biogenic amines metabolism in central nervous system.