In a previous study the stratum corneum of parakeratotic lesions was found to contain more sulfhydryl and less disulfide than normal. Furthermore, mucoprotein substances could be demonstrated in the pyknotic nuclei. Also, occasionally small clumps of these substances were seen in the parakeratotic layers. Finally, the parakeratotic strata seemed to contain ribonucleic acid. The present study was undertaken for the purpose of investigating the nucleic acids, carbohydrates, and sulfur compounds in hyperkeratoses and to compare the findings with those in parakeratoses. Material and Methods The material examined included (1) inflammatory lesions (lichen planus, acute and chronic dermatitis, lupus erythematosus discoides, pityriasis rosea); (2) proliferative lesions (calluses, seborrheic keratoses, keratotic nevi, verrucae vulgares, verrucae planae, papillomas, condylomas); (3) ichthyosis vulgaris, and (4) premalignant lesions (senile keratoses, leukoplakias, and x-ray keratosis). It was thought that this selection might disclose specific histochemical characteristics of