The symptoms ascribed to human adenomyosis are pain, especially with menstrual periods, cramps, and abnormally prolonged and profuse bleeding, while this lesion is also considered to be one of the causes of sterility in humans and animals. In this chapter, the authors aim to describe the general features of experimentally induced adenomyosis in mice, especially to elucidate the cause of the development of this lesion in relation to human cases. They develop an efficient induction method of uterine adenomyosis, in which young female mice are given transplants of isologous anterior pituitary glands into various sites remote from hypothalamus. Information of the histogenesis of adenomyosis was limited because of the lack of adequate animal models. In mice, pituitary transplantation always results in a significant increase of circulating prolactin levels; the levels rise within 3 weeks after the grafting, to the levels during pregnancy.