The effects of 17β-estradiol benzoate (EB) on the homotypical and heterotypical sexual behavior of male rats were studied. Lordosis was readily induced by daily administration of EB for periods of a week or more, commencing one week after castration. Intact males were somewhat less responsive. Estrogen-induced lordosis in the male differed from that in the female in the following respects: 1) Large doses of EB were required in the male. 2) The responses were less consistent in the male than in the female. 3) The effects of submaximal EB doses were not facilitated by progesterone, even when as much as 5 mg was used. Large doses of EB suppressed the homotypical behavior of normal males, but had a slight stimulatory effect in long-term castrates. When EB was administered from the time of castration, it produced “androgenic” effects on homotypical behavior. Some maintenance of ejaculatory patterns was observed, and the effects on intromission latency, intromission frequency and post-ejaculatory interval resembled those of testosterone. The testosterone-like stimulatory effects of EB on homotypical behavior of male rats are apparently masked in intact animals by its powerful gonadotropin-inhibitory effect. (Endocrinology84: 1365, 1969)