Based on the analysis of the dependence of 4-pyridoxic acid urinary excretion from pyridoxal-5'-phosphate blood plasma level and its statistic distribution it has been shown that vitamin B-6 metabolism in children suffering from phenylketonuria and therefore the criteria of the body saturation with this vitamin differ from those for healthy people. Increased pyridoxal-5'-phosphate blood plasma level has been demonstrated for PKU children. The concentration of 11 ng/ml should be considered as a bottom border of the adequate supply with vitamin B-6. The elevated vitamin B-2 intake approximates vitamin B-6 status indexes of sick children to those usually measured in healthy children. The necessity for the reevaluation of vitamin B-2 and B-6 optimal diet content under this disease and its biochemical validation are discussed.