The quantities of total and each flavin, and the activities of D-amino acid oxidase in the liver and kidney of vitamin D deficient, vitamin D administered rats and rats fed on standard diet were studied. Total flavins in the vitamin D deficient group was almost the same as those of the control (vitamin D deficient diet+vitamin D). However, in the normal group (fed on standard diet) higher levels of flavins than these two groups were found. In separative determinations of flavins, FAD of vitamin D deficient group were lower than that of the other. Activities of D-amino acid oxidase of these three groups were compared with each other and lower activities were found in the vitamin D dificient group.