Human chorionic gonadotropin (hCG) is a heterodimeric glycoprotein hormone consisting of a shared glycoprotein-hormone α-subunit and a distinct β-subunit that determines receptor specificity. The intact heterodimer binds the luteinizing hormone/choriogonadotropin receptor (LHCGR), a Gs-protein-coupled receptor expressed on testicular Leydig cells and ovarian theca and luteal cells. Ligand occupancy stimulates adenylyl cyclase, raises intracellular cyclic AMP, and activates protein-kinase-A-dependent phosphorylation of transcription factors and steroidogenic proteins, including steroidogenic acute regulatory protein (StAR) and cholesterol side-chain-cleavage enzyme (CYP11A1). In primary Leydig-cell cultures, testicular explants, and in-vivo rodent models of gonadotropin deficiency or experimental hypogonadism, exogenous hCG elicits measurable increases in testosterone (or progesterone) secretion and permits quantitative analysis of receptor-activation kinetics, desensitization, and hypothalamic–pituitary–gonadal-axis feedback under defined experimental conditions.