Development of uterine adenomyosis was studied in SHN mice treated with psychotherapeutic drugs, sulpiride and perphenazine, and gastroenteric drug, metoclopramide, which act as dopamine antagonists to increase prolactin release from the pituitary gland. Administration of these drugs twice daily for 40-70 or 40-90 days of age induced an elevation in serum level of prolactin. Furthermore, the treated mice showed a prolongation of metestrous plus diestrous phase and a high incidence of uterine adenomyosis compared with vehicle-treated control mice. These results indicate that hyperprolactinemia produced by continuous treatment with psychotherapeutic and gastroenteric drugs is responsible for the occurrence of irregular estrous cycles and the genesis of uterine adenomyosis in mice.