The effect of streptozotocin-induced diabetes mellitus on some parameters of energy metabolism and functional status of cell membranes was studied in experiments on rats. It was found that the development of diabetes mellitus is associated with dramatic changes in the metabolism of blood cells and kidney tissue: inhibition of aerobic ATP synthesis, accumulation of lactate, uncoupling of oxidative phosphorylation, and development of lactic acidosis. Diabetes mellitus leads to restructuring of membrane lipids, changes in microviscosity, and suppression of insulin receptors and membrane-bound Na(+), K(+)-ATPase, and Ca(2+)-ATPase. Sharply increased levels of LPO products and lactic acidosis during DM indicate an imbalance in the LPO-antioxidant system and development of oxidative stress.