Glucocorticoid hormone action in target tissues is modulated by 11b-hydroxysteroid dehydrogenase (11b-HSD), which catalyzes the interconversion of hormonally active C11-hydroxylated corticosteroids (cortisol, corticosterone) and their inactive C11-keto metabolites (cortisone, 11-dehydrocorticosterone). At least two isoforms of 11b-HSD exist: a low-affinity NADP-dependent dehydrogenase/oxoreductase (11b-HSD1) and a high-affinity NAD-dependent dehydrogenase (11b-HSD2). The glycosylated 11b-HSD1 protein activates cortisol from cortisone, which is widely expressed in mammals, and is most highly expressed in the liver. 11b-HSD1 may play a role in glucose homeostasis and pathogenesis of a number of disorders including insulin resistance and obesity.