The authors studied the chronic effect of ethanol on the functional state of creatine kinase system in myocardial mitochondria of adult rats. Mitochondrial functions were determined in skinned fibres prepared according to Veksler without mitochondria isolation. Compared with control values, ethanol was found to decrease statistically significantly the velocity of creatine-stimulated mitochondrial respiration (Vcr) and that of maximum ADP-induced stimulation of mitochondrial respiration (Vmax). The chronic action of alcohol also reduces the respiratory activation by creatine (%Cr) which ranks among the most sensitive indicators of mitochondrial respiration regulation by creatine kinase. The authors have demonstrated that the function of the creatine kinase system of myocardial mitochondria is impaired in alcoholic cardiomyopathy in the adult rat.