In order to investigate the relationship between the increment of plasma prolactin (PRL) levels and the change of plasma levels of PRL, DHEA-S, cortisol, aldosterone and 17 alpha OH delta 5-P were quantified by respective RIA in patients treated with TRH parenterally or with sulpiride orally. The results were as follows: During the infusion of TRH, plasma levels of PRL reached the maximal values within 30 min and then declined gradually in spite of continued TRH stimulation. Sulpiride given orally for 12 consecutive days in the luteal phase of the menstrual cycle caused a significant increase in the plasma PRL level. This increase was higher than that obtained in the experiment during the follicular phase. No significant change in the plasma level of 17 alpha OH delta 5-P was observed TRH sulpiride administration. In 3 out of 9 cases, plasma DHEA-S levels were elevated significantly on day 13 to 14 of the experimental course. These results indicate that the responsiveness of plasma levels of adrenal androgens to the raised plasma PRL level requires a certain period of time in the hyperprolactinemic state in the human female.