Testosterone (T) is known to play an important masculinizing role in the developing brain of rat, including the regulation of 5α-reductase (5α-R) isozymes. However, the effects of dihydrotesterone (DHT), a more potent androgen than T, have not been elucidated. In this study, DHT was administered from day 5 through day 20 of postnatal life (period of postnatal sexual differentiation of the central nervous system) at doses of: 12 mg/kg/d on days 5, 6, 7, 8, 19, and 20; 15 mg/kg/d on days 9, 10, 11, 12, 16, 17, and 18; and 18 mg/kg/d on days 13, 14, and 15. In adulthood, quantitative RT-PCR was used to measure mRNA levels of 5α-R1 and 5α-R2 isozymes in the prefrontal cortex (PFC) of male and female rats with varied androgenic status. Under our study conditions, neonatal DHT administration influenced on adult PFC 5α-R isozymes levels and their regulation pattern by androgens, and this pattern was the inverse of that reported in adult neonatally T-treated rats.