Regional differences in the androgen metabolism were established in alopecic and non alopecic areas of patients affected by male pattern baldness (MPB). 5-alpha-reductase (5-alpha-R) activity was measured by the formation of dihydrotestosterone (DHT), using 3H-testosterone as substrate: this activity was higher in the alopecic areas (3.4 pmol/g tissue/h) than in the non alopecic skin (1.5 pmol/g tissue/h). 3-alpha,beta-hydroxysteroid oxoreductase (3-alpha, beta-HO) was studied using 3H-DHT as precursor and measuring the corresponding formed 3-alpha- and 3-beta-androstanediols (alpha DIOL and beta DIOL). The beta DIOL was the predominant metabolite and total 3-alpha, beta-HO activity was higher in alopecic skin (12.4 pmol/g tissue/h) than in non alopecic areas (8.4 pmol/g tissue/h). Also 17, beta-hydroxysteroid oxoreductase was measured using either testosterone or DHT as substrates: androstenedione formed from testosterone was higher in hairy skin (12 pmol/g tissue/h) than in alopecic areas (6 pmol/g tissue/h); androstanedione formed from DHT was also higher in non alopecic areas (8.1 pmol/g tissue/h) than in alopecic skin (2.8 pmol/g tissue/h). The greater formation of beta DIOL in the sebaceous glands-enriched alopecic skin supports the hypothesis for a specific role of this metabolite in the control of the sebaceous activity.