The literature reveals contradictory data regarding whether or not male release LH acutely following coitus. Since it has been shown that repeated mating increases accessory sex organ weight, suggesting induction of gonadotrophin release, it seemed of interest to reinvestigate the issue. Male rats were divided into two groups: the mated group was provided with frequent mating ("experiencing") trials; the unmated group served as cage controls which received no sexual contact throughout the entire experiment. All rats were provided with chronic jugular cannulae. One set of serum samples was taken from each rat at 85 days, the second set at 115 days. On the two evening when sampling took place the mated rats were subdivided into three groups: "chamber" (placed in mating arena alone), "mount" (allowed two to five mounts, but no intromission), and "ejaculation" (mated through entire copulatory sequence). Serum sampling took place every 15 min during the hour following completion of mating (defined in the "ejaculation" group). On the day following the second sampling, autopsies were performed, and terminal serum samples were taken. LH, FSH, and prolactin were measured by radioimmunoassay. There were no significant differences in any hormone among the groups during the hour following mating nor in the terminal sample. However, the mated rats showed significantly greater seminal vesicle and ventral prostate weights than the cage controls at autopsy. Several hypotheses are offered to account for the latter findings.