Abstract The dorsal raphe nucleus was destroyed (DRL) by a radiofrequency lesion generator in castrated male rats, and lordosis behavior was observed. Five weeks after the surgery, all animals were implanted with two Silastic tubes containing estradiol (E 2). Behavioral tests were started 2 days after implantation of E 2 and carried out every other day for 16 days. Castrated control and sham-operated control males showed low incidence of lordosis and low lordosis quotient (LQ) throughout the tests, whereas all the DRL males displayed lordosis and the mean LQ of the group was significantly higher than that of control groups, but lower than that of an ovariectomized female group. These results suggest that the dorsal raphe nucleus plays an important role in inhibiting lordosis in male rat brain.