Production rates of testosterone (T) and of dihydrotestosterone (DHT) were determined in young women (n=8, age, 23 to 40 years) with female-pattern hair loss using the stable isotope dilution technique and mass spectrometry. 1 alpha,2 alpha-d-testosterone and 2,3,4-13C-dihydro-testosterone were infused for 10 hours at a dose of 2 microg/h each and blood samples were obtained at 20-minute intervals during the last 4 hours of the observation period. In the presence of normal metabolic clearance rates (MCRs), production rates of T were increased (9.4+/-5.0 microg/h; normal, 4.3+/-1.9 microg/h, P<.05). MCRs of DHT (8.0+/-3.4 L/h; normal, 25.9+/-12.3 L/h, P<.002) were subnormal in all women and the production rates of DHT were within or below the normal range (mean, 1.6+/-0.6 microg/h; normal, 2.9+/-1.1 microg/h, P<.02). Unlike men with male-pattern baldness, women with female-pattern baldness are characterized by increased production rates of T, but not of DHT. These results are compatible with the idea that 5 alpha-reductase inhibition is of no therapeutical value in female-pattern baldness.