Studies were conducted to determine if the inhibitory effects of chronic hyperprolactinemia on sexual behavior in male rats occur through reduced sexual arousal as opposed to reduced erectile function. Pituitary-grafted (hyperprolactinemic) and sham-operated, gonadally intact male rats were given standard tests of copulatory behavior, mounting behavior tests after genital anesthetization and penile reflex tests while restrained in a supine position. Beginning 7 days after pituitary transplantation, the number of erections displayed in penile reflex tests was significantly reduced in the pituitary-grafted animals. Increased intromission latencies and reduced intromission rates in tests of copulatory behavior were also observed at this time. Beginning 3–4 weeks after surgery, mounting rates were inhibited in hyperprolactinemic animals in both the copulatory behavior tests and tests of mounting behavior after genital anesthetization. Prolactin levels were significantly elevated in the pituitary-grafted animals, but serum testosterone levels were unaffected. To determine if the effects of hyperprolactinemia on erectile function occurred through changes in supraspinal input to neurons in the spinal cord controlling erectile function, pituitary-grafted and sham-operated male rats were subjected to spinal transection (between vertebral levels T6 and T9). Beginning 7 days later, penile reflex performance was re-examined. Hyperprolactinemic animals displayed significantly fewer erections during the initial test, but not in tests performed 10 and 13 days after spinal transection. The pituitary-grafted animals also showed a significant reduction in latency to the first erection with each successive test, suggesting a delayed recovery from increased supraspinal inhibitory input. These results show that hyperprolactinemia inhibits both sexual arousal and erectile function, and suggest that the inhibition of erectile function occurs through an effect of the hyperprolactinemic state at a supraspinal level within the central nervous syste