5-a-Dihydrotestosterone (DHT) is a C19 androgenic steroid hormone similar to testosterone and androstenedione. The bulk of the androgen production takes place mainly in the Leydig cells of testes.

Androgens circulate in the blood bound to proteins, especially Sex hormone binding globulin (SHBG) and albumin. A trace amount of these steroid in the unbound form in the blood and are referred to as the free fractions. DHT has at least times the binding affinity for SHBG than testosterone. In males about 70% of DHT is derived from peripheral conversion of testosterone. However, in females most of the DHT is derived from the androstenedione.DHT is produced by males in vivo and is responsible for the formation of male sex-specific characteristics. DHT is an important contributor to other characteristics generally attributed to males, including facial and body hair growth, and deepening of the voice.