Parakeratosis is so characteristic and occurs in so many skin diseases that an adequate knowledge of its histochemistry appears indispensable. Nevertheless, many histochemical characteristics of parakeratosis still are largely unknown. The following study was undertaken to investigate some of these characteristics. Beginning with Giroud and his collaborators, in 1929, several investigators used different stains for the determination of sulfhydryl (SH) in normal and abnormal epidermis. All of these stains revealed more SH in the parakeratin than in the viable epidermal cells and much more than in normal keratin (Percival and Stewart, Lapière, Hollander et al., Zingsheim, and others). However, prior to Barrnett and Seligman's dihydroxy-dinaphthyl-disulfide (DDD) reaction supplemented by thioglycolic acid (1954) no histochemical estimate of the total sulfur was possible, i. e., of disulfides (SS) as well as of SH. This estimate, however, appears to be important because of the following reasons. Observations with DDD