Female rats were given a single subcutaneous injection of either 10 or 100 μg testosterone propionate (TP) or dihydrotestosterone propionate (DHTP) on Day 1 or 5 of life (Day 1 = day of birth). Both TP and DHTP delayed vaginal opening on Day 1 and advanced vaginal opening on Day 5. Testosterone propionate, but not DHTP, induced constant vaginal cornification and polyfollicular ovaries in the majority of rats. Dihydrotestosterone propionate had no effect on the Receptivity Quotient (lordosis/mount ratio × 100), whereas 100 μg TP on Day 1 or 5 significantly lowered the Quotient compared to DHTP treatment. Both TP and DHTP were equally potent in preventing ovarian compensatory hypertrophy in unilaterally ovariectomized female rats. In addition, treatment with 200 μg DHTP daily did not prevent the ovarian weight increase in response to exogenous gonadotrophin. The significance of these observations are discussed with respect to the physiological rôle of DHT.