Prolactin was isolated and identified as a separate pituitary hormone distinct from human growth hormone. Since that time a rapidly expanding literature has accumulated on the physiology of pituitary prolactin secretion in normal and pathologic conditions. Currently the physiology and pathophysiology of pituitary prolactin secretion are under intensive investigation. Development of sensitive, specific radioimmunoassay for prolactin and improved roentgenographic techniques have increased the diagnostic acumen for incipient pituitary microadenomas. Dynamic function tests of prolactin secretion have not helped to distinguish whether a patient has a microadenoma or not. The basal prolactin level is probably the most useful single investigation for diagnosis a pituitary tumour. If women with pituitary tumours have ovulation induced with bromocriptine therapy, then there is a considerable risk of rapid enlargement of the tumour with the development of serious visual field defects often during the last trimester. The precise level of the risk is not clear, but is probably not great. The introduction of bromocriptine has heralded a major change in the menagement of the hyperprolactinaemia-hypogonadism syndromes and resulted in safer and easier treatment of many cases of infertility, menstrual disorders and, to a lesser extent of impotence. At present, bromocriptine therapy is the treatment of choice for hyperprolactinaemia.