Patients with primary infertility due to hyperprolactinemic corpus luteum insufficiency and oligomenorrhea were treated with Bromocriptin. Suppression of serum prolactin for up to four menstrual cycles resulted in a normalisation of the length of the cycle(32 vs 28 days) as well as of luteal progesterone secretion. In addition, ovulation occurred earlier after than before treatment (on day 14 vs day 18). When, however, prolactin concentrations reached levels of less than 120 muU/ml (3 ng/ml), which were observed during the 5th and 6th treatment course, reappearance of shortened luteal phase occurred probably due to oversuppression of prolactin. Premenstrual spottings were observed too. The data presented indicate that minimal prolactin is required for normal follicular maturation and luteal development. On the other hand, the gonadostat may be susceptable to the dopaminergic stimulus of Bromocriptin to a different extent as oversuppression of prolactin is not observed in hyperprolactinemic anovulatory syndromes. Thus, treatment with Bromocriptin requires a continuous monitoring of serum prolactin as well as individual treatment regimens.