In order to assess an influence of estrogen and TRH on prolactin secretion, TRH stimulation tests were performed in fourteen hypogonadal women, which included 8 postmenopausal and 6 obariectomized cases, before and after administration of conjugated estrogen at a dose of 1.25 mg per day for four weeks. The results of of this study are as follows: 1. There was a significant elevation of baseline serum prolactin levels after the estrogen treatment, but baseline serum TSH levels did not reveal a significant difference. 2. After estrogen treatment, a significant further rise in prolactin reponse to TRH test than that of the pre-estrogen treatment were noted. 3. After the estrogen treatment, the serum levels of FSH and LH returned to their usual premenopausal levels without any significant influence from the TRH test. 4. These data suggest that pituitary gland has a functional capacity to secrete prolactin though the ingluence of estrogen and TRH in hypognadal women.