Light and electron microscopical studies have been performed on the cutaneous lesions of the rats fed on vitamin A deficient diet. Histologically, the skin of the vitamin A deficient rats revealed marked atrophy of the epidermis, loss of the granular layer and follicular hyperkeratosis with keratotic plugs. In the epidermis no clear difference between the basal and the prickle cells was demonstrated. In these cells remarkable vacuolar appearance in the cytoplasma and pyknotic change in the nuclei were observed. The dermis showed slight edema and the swelling of the collagen fibers was slight but demonstrable. Marked decrease and atrophy of the hair follicles and the sebaceous glands were observed. The subcutaneous fatty tissue also disclosed marked decrease. Electron microscopical observation exhibited demonstrable changes of the mitochondria in the cytoplasma of the basal and the prickle cells, such as swelling, lower density, vacuolar formation, and irregularity in size and form. Vacuolar formation in the cytoplasma was observed. Desmosomes were intact but the intercellular spaces in the prickle layer were narrow. Tonofibrils attached to desmosomes were short. Decrease in number and size of tonofibrils and keratohyalin granules was also noticed, moreover disappearance of the latter was encountered in many cases. Odland body in the upper prickle cells could not be detected in many cases. Normal keratin pattern of the horny layer was not observed and a curtain lace like structure between the horny and the prickle layers was seen.