Changes in intracavernous pressure (ICP) were recorded in freely moving rats by means of a catheter implanted in the corpus cavernosum and connected to a pressure transducer located subcutaneously. Intracavernous pressure changes and copulatory events (mounts, intromissions and ejaculations) were recorded during several overnight testing sessions with 12 rats in the presence of receptive females. Video recordings of sexual behavior in the implanted and nonimplanted rats revealed that the ICP device did not impair copulatory behavior. Comparison between copulatory behavior and ICP changes revealed that ICP profiles could identify the number of intromissions and ejaculations as well as the timing of these events. The results showed that during mounts, intromissions and ejaculations, ICP increases were 36.9 mm. Hg, 62 mm. Hg and 106.3 mm. Hg in 4 rats. The increases in ICP during mounts and intromissions appeared higher in sexually experienced as compared with sexually naive rats. These results demonstrate the reliability of the telemetric measurement of ICP in freely moving rats under natural physiological conditions. The model provides quantitative data for research on the neurophysiology of penile erection and evaluation of oral treatments for impotence.