The Wistar rat represents a very useful model in experimental surgery and in scientific research. The anatomic structures are very similar to those encountered in man. Moreover the cost for their purchase, breeding and nourishment is very low and it's possible to perform surgical maneuvers without sterility. Nevertheless the penis has an extremely small dimension and its anatomic structure is quite different from that of man because corpora cavernosa are almost completely occupied by an osteo-cartilagenous formation: the os penis. For this reason it's very difficult to perform a physiopathological study of erection on the rat. On the other hand the nervous fibres are very similar for course and localization to those encountered in man and monkeys. Their electrical stimulation causes an erection which is adequate in duration and intensity to be evident.