Uterine adenomyosis is a benign lesion but a serious disease for women, because the symptoms are characterized by abnormal bleeding, pain, cramps, and sterility. Thus elucidation of the mechanisms involved in the development of the disease would contribute to improved management and treatment and prophylaxis of this lesion. A mouse model, in which ectopic pituitary isografting is associated with an increase in the plasma level of prolactin, is useful for a rapid and frequent induction of uterine adenomyosis and can be used to study the origin of this lesion.