It is note that hyperprolactinemia is frequently associated to chronic renal failure (CRF). The etiopathogenesis of this endocrine disorder is not clearly understood, trying to evaluate the possible hypothalamic-pituitary cause we have evaluated the Prl levels under some pharmacological tests: TRH (200 mcg i.v.),Domperidone (DOM)(10 mg i.v.),Nomifensine (NOM)(200 mg p.o.)and Bromocriptine (BRC)(2.5 mg p.o.) in 3 groups of patients: CRF(8 cases), dysfunctional (8 cases) and tumoral (9 cases) hyperPrl. Prl plasma levels have been evaluated by RIA (kits,Biodata,Roma). In patients affected by CRF either direct (BRC) than indirect (NOM) agonist acting dopaminergic drugs failed to induce a reduction in Prl plasma levels, like to tumoral patients for NOM, and in contrast to the significant decrease after BRC (-70%) in tumoral and (-74%) in dysfunctional and NOM (-50%) observed in dysfunctional patients. CRF and dysfunctional patients showed significant response to TRH and DOM, being prolactinoma bearing patients unresponsive to these tests. These results show an hyporesponsivity of pituitary Prl secreting cells to dopaminergic control suggesting the existence of central etiopathological factor in inducing hyperprolactinemia in CRF patients.