From the data presented it appears that ergot drugs are both a useful tool for use in the study of neuroendocrine control of pituitary hormone secretion and a valid pharmacologic weapon for treatment of hyperprolactinemic states, GH and, probably, ACTH and MSH hypersecretion. In fact, they are capable of a long-lasting disruption of PRL secretion from a normal or tumoral pituitary gland, are unable to affect directly the somatotrophs of an intact AP, but inhibit GH and, possibly, ACTH secretion from a hyperplastic or tumoral gland. Ergolines also exert clear-cut PRL-lowering effects and are capable of suppressing GH secretion in acromegaly. The intimate mechanism(s) and hence site(s) of action of some of these compounds await clarification.