Histological and histochemical investigations were undertaken on gonads, chiefly on testicles, of pyridoxine deficient rats. The effects of pituitary gonadotrophine of pyridoxine deficient male rats were also studied. The tisticles or ovaries and accessory sex organs of pyridoxine deficient rats were remarkably atrophic. The atrophy of the testicles of pyridoxine deficient rats could not be completely prevented but slightly restored by gonadotrophine administrations. The atrophy of testicles in the pair weighted control was slight. It was concluded that the atrophy of gonads in pyridoxine deficient rats was caused chiefly by metabolic disturbances in the gonads due to pyridoxine deficiency and partly by dysfunctions of the pituitary and slightly by chronic inanition.