Hyperandrogenism, a main clinical feature of polycystic ovary syndrome (PCOS), is thought to result from enhanced ovarian and adrenal androgen generation. To investigate the contribution of peripheral steroidogenesis, we used an oral challenge with dehydroepiandrosterone (DHEA) and analyzed its downstream conversion toward androgens in eight women with PCOS (age, 20–32 yr; body mass index, 20–41 kg/m²) and eight healthy women matched for age and body mass index. They underwent frequent serum sampling and urine collection for 8 h on three occasions: at baseline, and after 4 d of dexamethasone (Dex; 4 × 0.5 mg/d), followed by ingestion of 100 mg DHEA or placebo. Dex induced similar significant suppression of circulating steroids in both groups. The oral DHEA challenge led to similar significant increases in the area under the concentration-time curve (0–8 h after Dex) of serum DHEA, DHEA sulfate, androstenedione, and testosterone. However, after oral DHEA, PCOS women had significantly higher increases in serum 5α-dihydrotestosterone (P < 0.01), its main metabolite androstanediol glucuronide (P < 0.05), and the 5α-reduced urinary androgen metabolite androsterone (P < 0.05). PCOS women also had significantly higher baseline excretion of 5α-reduced glucocorticoid (P < 0.01) and mineralocorticoid metabolites (P < 0.05). Taken together, these data indicate enhanced peripheral 5α-reductase activity in PCOS. Thus, not only ovary and adrenal, but also liver and peripheral target tissues, significantly contribute to steroid alterations in PCOS.