Department of Medicine III and Clinical Endocrinology, University Hospital 'Dijkzigt', Erasmus University, Rotterdam, The Netherlands (Received 16 February 1976) The role of catecholamines in modulating the secretion of adrenocorticotrophin (ACTH) has been investigated by numerous workers with conflicting results (van Loon, 1973). In some of these studies l-DOPA has been used, which induces the production of adrenaline and noradrenaline in addition to that of dopamine. Recently 2-bromo-α-ergocryptine became available; this drug seems to be a more specific activator of the dopaminergic pathways in the central nervous system (Corrodi, Fuxe, Hökfelt, Lidbrink & Ungerstedt, 1973). On the basis of a recent observation, that the daily administration of 0·05 mg ergotamine to rats bearing ACTH-secreting pituitary tumours inhibited tumour growth and reversed adrenal enlargement (Macleod & Lehmeyer, 1973), we investigated the effect of bromocriptine on plasma ACTH levels in seven patients with pituitary-dependent Cushing's syndrome (one with a pituitary tumour) and four