11-Ketotestosterone (11-KT) is an oxidized form of testosterone that contains a keto group at the C11 position. It is related to adrenosterone, an androgen found in trace quantities in humans. In fish, 11-ketotestosterone functions as the endogenous androgenic sex hormone. In midshipman fish, 11-ketotestosterone is not present in females or Type II Males — Type II Males reach sexual maturation later, are less territorial, and have higher testosterone than Type I Males.
In mammals, 11-ketotestosterone has similar potency to testosterone as an androgen, and has been identified as an important adrenal androgen. It is synthesized from 11β-hydroxyandrostenedione and, to a lesser extent, 11-ketoandrostenedione (adrenosterone). 11-Ketoandrostenedione has notably been sold online as an androgen prohormone, usually under the name 11-oxoandrostenedione (11-OXO).