The ultrastructural localization of TPPase and AcPase in rat skin was studied. AcPase appeared localized in the lysosomes of the basal layer and in the keratinosomes of spinous, granulous and corneum layers. A diffuse reaction was also present in the granulous cells cytoplasm. Only the keratinosomes in the superficial layer were TPPase positive, specially those of the intercellular spaces of the proximal horny cells. The Golgi apparatus of all skin cells reacted strongly towards TPP. Membranous structures with TPPase and AcPase activity were evident within horny cells and seem to be infolded portions of the cell membrane which keep their enzymatic activity.