Studied sexual exhaustion of 12 sexually experienced Long-Evans male rats with respect to several copulatory measures. The ejaculatory latency, intercouplatory interval, and intromission frequency demonstrated 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) increased linearly, whereas the relative refractory period (the remaining portion of the postejaculatory interval) was a positively accelerating function. Partial recovery tests demonstrate that the preejaculatory measures and absolute refractory period substantially returned to baseline values by Day 6, while the relative refractory period was still extended. The significance of these data to the theoretical modeling of sexual behavior is discussed. (18 ref) (PsycINFO Database Record (c) 2006 APA, all rights reserved)