The experimental findings showed that antidiabetic drugs influence the systems of metabolism of xenobiotics. Insulin, bucarban, glybenclamide, adebit enhance processes of hydroxylation in intact animals. Insulin deficiency in modelled diabetes mellitus produces a weakening of the above processes and administration of the hormone in a therapeutic dose causes normalization of processes of acetylation and hydroxylation. Insulin and glybenclamide enhance processes of acetylation in healthy animals, bucarban and adebit being inductors of microsomal oxidation do not produce such changes. Therefore, in clinical practice one should take into consideration these effects of the antidiabetic drugs in a complex therapy of diabetes mellitus.