Abstract: In order to assess the dependence of the thyroid status of the organism on the functional state of the monooxygenase system of the endoplasmic reticulum of hepatocytes in sexually mature male rats, induction and inhibition of the monooxygenase system of the liver by its inductors and inhibitors was caused. As inducers, we used known induction drugs - benzonal (benzobarbital) and zixorin (flumecinol), and as inhibitors a chemical compound - cobalt chloride and a blocker of histamine H2-receptors - cimetidine. Benzonal was administered orally at a dose of 50 mg / kg body weight for 3 days, and zixorin was administered at a dose of 40 mg / kg body weight for 4 days. Cobalt chloride was administered once intraperitoneally at a dose of 30 mg / kg of body weight, and cimetidine was administered orally at a dose of 100 mg / kg for 10 days. It was revealed that during the induction of the monooxygenase system of the liver by its inductors - benzonal and zixorin, there is an increase in the content of thyroid hormones - triiodothyronine and thyroxine in the blood against the background of no change in the level of thyroid-stimulating hormone. When the monooxygenase system of the liver is inhibited by its inhibitors - cobalt chloride and cimetidine, an increase in the content of thyroid hormones - triiodothyronine and thyroxine in the blood is also observed, but against the background of a statistically significant decrease in the content of thyroid stimulating hormone. It is concluded that there is an indirect relationship between the functional state of the monooxygenase system of the liver and the thyroid status of the body.