[Differentiation of external genitalia and 5 alpha-reductase].

: Sexual differentiation of the external genitalia depends on many factors such as genetic sex, gonadal sex or androgen action. Among them, 5 alpha-reductase plays an important role in androgen action: dihydrotestosterone(DHT) is produce from testosterone by 5 alpha-reductase and DHT binds the androgen receptor to induce the differentiation of the external genitalia. In this paper we reviewed on the mechanism of the differentiation of the external genitalia, especially on the relation with androgen action and 5 alpha-reductase.