Prolactin was determined by radioimmunoassay in the serum of 112 patients with primary or secondary amenorrhoea. 21 cases showed hyperprolactinaemia with levels above 25 ng/ml (18.7%). 10 patients with levels between 25 and 50 ng/ml showed heterogeneous clinical features. In nine women (8%) the prolactin level was above 100 ng/ml; they all had severe amenorrhoea. As a result of treatment with bromocriptine menstrual bleeding occurred in 4 out of 7 cases and 2 of these patients became pregnant. In 3 cases prolactin did not return to normal levels and in 2 out of these patients microadenomas of the pituitary gland were diagnosed by special methods. They were removed surgically by the transsphenoidal approach.