State of liver mitochondria from rats with alloxane diabetes and the organelles polyenzyme systems were studied in correlation with glucose content in blood. At the initial and middle steps of the diabetes liver mitochondria were able to synthetize ATP but the rate of substrates oxidation was decreased. In severe forms of the diabetes latent impairments were developed in mitochondrial membranes. The phenomenon was accompanied by a decrease in activity of NADH-, succinate- and cytochrome c oxidizing systems as well as by a distinct decrease in the rate of ATP synthesis. Incorporation of exogenous cytochrome c into mitochondrial membranes was impaired and the mitochondria became more susceptible to the effect of heating and of hydrolytic enzymes degrading the organelles.