Activity of enzymes responsible for creatine biosynthesis (transamidinase, EC 22.214.171.124., and guanidine acetate methyltransferase, EC 126.96.36.199.) was studied in homogenates of pancreas, kidney and liver tissue of mice in normal state and in hereditary muscle dystrophy (129/Re-dy). Simultaneously, the activity of guanidine acetate methyltransferase from liver tissue was studied after addition of glucagon and ardenaline. In normal healthy mice homogenates of liver tissue distinctly increased the activity of guanidine acetate methyltransferase if glucagon and adrenaline were used in physiological concentrations. At the advanced stage of mice hereditary myodystrophy liver homogenates lost their capacity to activate the enzyme after addition of the hormones. The data obtained suggest that adenyl cyclase is impaired in plasmatic membranes of liver tissue, which mediated, using cAMP,the transformation of hormonal signals affecting the intracellular synthesis of creatine.