Ten patients suffering from endometriosis were treated with danazol at a dose of 200 mg three times daily for 6 months. For evaluation of prolactin (PRL) and TSH secretion, a TRH test was carried out in the follicular phase before treatment, during the 6th month of treatment and after the reappearance of the second menses. The same test was also performed, only once, in the follicular phase of 10 normal women. The absence of a significant difference in the basal PRL levels as well as its response to the TRH test between controls and patients with endometriosis before and after danazol treatment supports the view that hyperprolactinemia should not be considered a cause of infertility in endometriotic women. Furthermore, there were no statistically significant changes in the basal levels of serum TSH during danazol treatment. On the contrary, in the TRH test, the response of serum TSH was significantly higher during danazol treatment than before or after treatment.