Male rats exposed to sexually receptive females, exhibit a rapid increase in plasma levels of luteinizing hormone (LH) and prolactin, and concomitant increases in noradrenergic activity in the medial basal hypothalamus (MBH) and median eminence (ME) as well as in dopaminergic activity in the MBH. Delta-9-tetrahydrocannabinol (THC; 5 mg/kg b.wt., PO), the chief psychoactive constituent of marijuana, blocked the MBH and ME noradrenergic response and the dopaminergic response in the MBH in male rats exposed for 20 min to sexually receptive females, and suppressed the expected increases in plasma LH and prolactin levels. Moreover, THC treatment decreased the percentage of animals exhibiting copulatory behavior and increased the latency periods to mount and intromit. These findings indicate that THC interferes with the neuroendocrine and behavioral responses of male rats to the presence of a receptive female.