Sexual exhaustion of the male rat was studied with respect to several copulatory measures. The ejaculatory latency, intercopulatory interval, and intromission frequency demonstrate a U-shaped curve, exhibiting high values for the initial ejaculatory series, falling to a minimum at an intermediate ejaculatory series, and again increasing at exhaustion. The absolute refractory period of the postejaculatory interval (measured at vocalization termination) increases linerly, whereas the relative refractory period (the remaining portion of the postejaculatory interval) is a postively accelerating function. Partial recovery tests demonstrated that the preejaculatory measures and absolute refractory period have substantially returned to baseline values by Day 6, while the relative refractory period is still extended. The significance of these data to the theoretical modeling of sexual behavior is discussed.