In the fronto—parietal scalp in androgenetic alopecia, hair follicles gradually become minuaturized, and the anagen period becomes shorter. Recent clinical findings clearly show that the type 2 isozyme of 5 α-reductase（5 αR2）, which converts testosterone to dihydrotestosterone, plays a crucial role in beard growth and the development of androgenetic alopecia. Patients with 5 αR 2 deficiency possess less facial hair and do not become bald. In addition, finasteride, a 5 αR 2 inhibitor, partially reverses hair loss in androgenetic alopecia. There is considerable evidence to suggest that the dermal papilla plays a key role in hair growth and mediates the action of androgen. 5 αR of cultured beard dermal papilla cells shows the characteristics of the type 2 isozyme；the isozyme pattern of 5 αR in those from balding scalp remains unknown. Follicular epithelium such as the outer root sheath and hair matrix exhibits the activity of 5 αR 1. Freshly isolated hair follicles, containing both epithelial and mesenchymal portions, have been shown to have both 5 αR1 and5 αR 2 activities, and those from balding scalp have three times higher activity of 5 αR 2 than those from the occipital scalp.