1. The formation of estradiol-17β is one of the pathways of the metabolism of T in the tissues of various regions of the brain of 21-day old rat fetuses (PVN, MPA, ACr, ACc, DVC). 2. DHT and 3α-diol are the principal metabolites of T in these regions of the brain. The formation of DHT predominates in terms of the quantitative ratio in the PVN, DVC, and ACr, while it is the formation of 3α-diol which predominates in the MPA and the ACc. 3. The intensity of the metabolism of T in the ACr is substantially higher than in the ACc. © 1991 Plenum Publishing Corporation.