Corticotroph-derived glycoprotein hormone (CGH), also referred to as thyrostimulin, is a non-covalent heterodimer of glycoprotein hormone alpha 2 (GPHA2) and glycoprotein hormone beta 5 (GPHB5). Here, we demonstrate that both subunits of CGH are expressed in the corticotroph cells of the human anterior pituitary, as well as in skin, retina, and testis. CGH activates the thyroid-stimulating hormone receptor (TSHR); ¹²⁵I-CGH binding to cells expressing TSHR is saturable, specific and of high affinity. In competition studies, unlabeled CGH is a potent competitor for ¹²⁵I-thyrotropin binding, while unlabeled thyrotropin does not compete for ¹²⁵I-CGH binding. Binding and competition analyses are consistent with the presence of two binding sites on the TSHR transfected BHK cells, one that can interact with either thyrotropin or CGH, and another that binds CGH alone. Transgenic overexpression of GPHB5 in mice produces elevations in serum T₄ (T4) levels, reductions in body weight, and proptosis. However, neither transgenic overexpression of GPHA2 nor deletion of GPHB5 produces an overt phenotype in mice. In vivo administration of CGH to mice produces a dose-dependent hyperthyroid phenotype including elevation of T4 and hypertrophy of cells within the inner adrenal cortex. However, the distinctive expression patterns and binding characteristics of CGH suggest it has endogenous biological roles that are discrete from those of thyrotropin.