In fresh human skin homogenates, the activities of four enzymes, lactate dehydrogenase (LDH), glucose-6-phosphate dehydrogenase (G-6-PDH), "acid" phosphatase (AcP), and "leucine aminopeptidase" (LAP) were assayed following an incubation with hydrocortisone, hydrocotisone acetate, or hydrocortisone-17-butyrate, respectively. Concentration of the three compounds measured 2.75 mMol/l. Hydrocortison butyrate inhibited LDH-G-6-PDH-, and AcP-activities. Hydrocortisone and hydrocortisone acetate exerted a significant inhibitory action only in the case of G-6-PDH-activity.--On pure G-6-PDH from yeast, the inhibition exerted by hydrocortisone butyrate was significantly stronger than the inhibition exerted by the two other steroids. Time/action diagrams revealed the fact that hydrocortisone butyrate is superior to the other two compounds from the beginning of the incubation period.--The date sustain the assumption that hydrocortisone butyrate exerts biochemical-pharmacological actions of its own and that it may not be considered just as an esterified transport form of hydrocortisone.