Since not all problems in endometriosis can be studied in the human, there is need of an animal model. We transplanted endometrial tissue of the rabbit into the peritoneal cavity and studied the changes after 12 weeks. At that time the endometrial implants in the rabbit had become cystic structures. The macroscopic and histologic appearance was consistent with endometriosis. Hormonal supplementation turned out not to be necessary. Microsurgical techniques prevented the formation of tubo-ovarian adhesions. This makes the rabbit model suitable for studying the influence of endometrial implants on fertility.