Studies are carried out on the changes during the hexobarbital sleep and the cholinesterase activity in male rats subject to multiple oral introduction of carbaryl in relative low doses (40 mg/kg daily). The changes in the hexobarbital sleep and the relative weight of the liver during the 21-day treatment with carbaryl (40 mg/kg) show acceleration of the biotransformation processes in the organism of 6-month male albino rats. The raised activity of the serum cholinesterase activity can be accepted as an expression of the reinforced synthesis of protein in the liver.