Wistar female rats were injected with testosterone (T) or 5 beta-dihydrotestosterone (5 beta-DHT) for the first 5 days of life. Neonatal treatment with 1 mg of T resulted in anovulatory persistent oestrous syndrome in 100% of the animals. In the females injected with 1 mg of 5 beta-DHT, 74% of the treated rats became sterile at 120 days of age. In addition, 0.5 mg 5 beta-DHT was also effective in inducing anovulatory persistent oestrus; the incidence of sterility was 10 and 80% at 60 and 120 days of age, respectively. When daily dose of 5 beta-DHT was reduced to 0.1 mg, however, only 33% of the rats resulted in sterility. These results suggest that the free form of T and non-aromatizable androgen, 5 beta-DHT, can permanently suppress the development of female type of neuroendocrine regulation. The possible participation of the process other than the central aromatization in androgenization will be discussed.