The activity of 17 beta-hydroxysteroid dehydrogenase (17 beta-HSD) was assayed in various tissues microdissected from the freeze-dried human skin of fourteen subjects. The apocrine sweat gland, sebaceous gland and hair follicle possessed a high activity of 17 beta-HSD. The enzyme activity was negligible in the epidermis, except that the scalp epidermis showed much the same activity as the hair follicle. The demis showed variable activity because of contamination with other components.