Tissue incubation was used to determine the production of prolactin by ectopic and eutopic endometrium from 29 patients with endometriosis. The concentrations of prolactin in media were detected by radioimmunoassay(RIA). Avidin-biotin immunoperoxidase method was used to demonstrate the presence of prolactin in ectopic and eutopic endometrium. Results:the levels of prolactin in media were significantly increased as ectopic and eutopic endometrial tissues incubated from 0 to 3 and to 24 h(P<0.05);yet,the contents of prolactin at 48 h in media were not increased. There was less secretory activity of prolactin in ectopic endometrium than in eutopic endometrium. Positive staining for prolactin was found in 4 ectopic endometria and 6 eutopic endometria. The histology showed that the more matured endometrial epithelial cells and predecidual cells,the higher concentrations of prolactin and the stronger prolactin staining. This suggested that secretive function of prolactin in ectopic endometrium was not the same as in eutopic endometrium,and it was related to pathologic environments.