The content of mitochondrial cytochromes and the activity of key enzymes of heme metabolism in the liver of rats under conditions of different dietary supply of protein and sucrose were investigated. The quantitative determination of mitochondrial cytochrome was performed by differential spectrophotometry, δ-aminolevulinate synthase activity was determined spectrophotometrically taking into account the molar extinction coefficient of 0.023x10(3) M(-1)sm(-1). Hemoxygenase activity was determined using the amount of formed bilirubin. It was found that under conditions of consumption of high-sucrose diet a significant decrease in the content of all mitochondrial cytochromes is noted: the content of cytochromes aa3, b and c1 decreases within 1.2-1.7 times, and content of cytochrome c decreases in two times. In the case of excessive consumption of sucrose on the background of alimentary protein deprivation the content of cytochromes b and c1 in the liver of rats does not differ statistically from similar indicators of the group of animals kept on a high-sucrose diet. At the same time, the content of cytochromes aa3 and c is significantly reduced. According to the activity of δ-aminolevulinate synthase under conditions of consumption of a high-sucrose diet, the studied enzymatic activity decreases by about 1.5 times with a simultaneous increase in the activity of heme oxygenase. Thus, there is a marked decrease in heme synthesis against the background of increased catabolism, which explains the decrease in the content of cytochromes in the mitochondria of the liver of rats under conditions of excess sucrose in the diet. The maximum increase in the activity of heme oxygenase (almost threefold) is observed in animals that were kept on a high-sugar diet deficient in protein content. Thus, dietary protein deficiency is a critical factor affecting the heme metabolism in the mitochondria of liver cells. The established changes in the content of mitochondrial cytochromes and the activities of key enzymes of heme metabolism in the liver could be considered as prerequisites for deepening its energy imbalance in conditions of different supply of sucrose and protein in diet.