Activity of tyrosine hydroxylase (TH) was detected in human thrombocytes. The TH and monoamine oxidase (MAO) activities were estimated in thrombocytes of patients with alcoholism of various clinical manifestations. Activity of TH was increased in patients with severe abstinence disorders; after termination of the syndrome the enzymatic activity was normalized. Activity of MAO, being at low level in the patients with abstinence and delirious syndromes, was markedly increased after discontinuation of the delirium syndrome. Reasons and consequences of the enzymatic activity alterations are discussed.