Abstract
The sex behavior of 12 rats reared in isolation was tested after they were 142 days old. One half received daily injs. of testosterone propionate beginning at 120 days of age. Test objects consisted of a small [female] guinea pig, a non-receptive [female] rat, a young [male] rat, an estrous [female] rat immobilized by the inj. of a general anesthetic and a sexually receptive [female] rat. The testosterone increased susceptibility to sexual excitement. Treated rats reacted more frequently than control rats to incentive animals of relatively low stimulus value.