It has been shown in experiments in v~vo that the use of phenazepam is accompanied by the appearance of hepatospecific enzymes of catabolism in the blood serum -histidlne and urokinase, not detected normally [7], and it has been noted that a single administration of phenazepam in a dose of 5 mg/kg leads to a substantial change in such parameters as the antioxidant activity of the lipids and the relative content of phospholipids [6], an increase in the specific content of cytochrome P-450 in the animal liver and the rate of demethylation of dimethylaniline [3]. The cause of this may be the injurious action of benzdiazepine tranquilizers on the liver [i].