Increase of vitamin B6 derivatives by 36% in liver tissue, decrease in content of thiamine by 20%, of ascorbic acid--by 35%, of oxidized nicotinamide coenzymes--by 27%, simultaneously with a decrease in excretion of 1-methyl nicotinamide and 4-pyridoxic acid with urine were observed in rats with alimentary deficiency in riboflavin as compared with the animals kept on a ration containing 1/3 of the vitamin physiological requirements. The same regularities were detected in adult persons and children examined for consumption of vitamins: a decrease in excretion of 4-pyridoxic acid and 1-methyl nicotinamide with urine, slight decrease in content of pyridoxal coenzymes in blood plasma and of nicotinamide coenzymes in erythrocytes were observed in children with deficiency in riboflavin close to deficiency of corresponding enzymes in food ration as compared with normal level of vitamin consumption. This suggests that evaluation of pyridoxine and/or niacin deficiency in food ration should be related with the rate of riboflavin consumption.