Twelve anovulatory patients with normal serum prolactin values and six with elevated values were treated with bromocriptine and the effects on serum prolactin, FSH and LH levels were recorded. Ovulation resulted in one patient who had normal prolactin values and in all six who had raised values. No patient with normal basal prolactin values showed an increase in serum FSH during therapy with bromocriptine, whereas 5 of the 6 patients with elevated values showed significant increases. Similar results were obtained for LH. Although these differences were highly significant (P less than 0-005) the majority of the serum FSH and LH values remained within the normal ranges. Five patients with normal basal prolactin values and one with elevated values were also treated with human pituitary gonadotrophin (HPG). An increase in ovarian responsiveness to HPG during therapy with bromocriptine was recorded in the one patient with initially elevated prolactin values. It was concluded that bromocriptine acts by allowing FSH to rise above threshold requirements for follicular stimulation.