In prolactinoma patients, the unresponsiveness of prolactin (PRL) to dynamic tests with thyrotropin-releasing hormone (TRH) or dopamine agonist or antagonist drugs suggests that the disease is caused by the failure of central dopaminergic inhibition. The absence of PRL secretory response to dopamine or TRH in prolactinoma patients also may be an effect of the disease. Twenty-six women diagnosed by dynamic tests and radiologic examination as having PRL-secreting adenoma were treated surgically (15) or with bromocriptine (11) and their condition was evaluated one to three years later by TRH, nomifensine, and domperidone tests. Basal PRL levels decreased after surgery and bromocriptine treatment. At the time of the follow-up study, PRL levels were elevated in six of the 15 surgically treated patients and in six of the 11 treated with bromocriptine. Thyrotropin-releasing hormone, nomifensine, and domperidone produced standard PRL responses in normoprolactinemic patients but not in hyperprolactinemic patients. These results indicate that the alteration of TRH or dopaminergic receptors in the regulation of PRL secretion in prolactinoma is related to the disease and disappears when the tumor is removed or treated successfully with bromocriptine.