The effects of sodium and potassium excretion after intrahypothalamic administration of two α-adrenoceptor agonists and the effect of α-adrenoceptor antagonists were studied in groups of rats. Prazosin was equally effective at blocking the natriuretic and kaliuretic responses to the α₁-adrenoceptor agonist phenylephrine and the mixed α₁/α₂-adrenoceptor agonist noradrenaline, while yohimbine which acts preferentially on α₂-adrenoceptors was effective in potentiating these responses. These results suggest the presence of two types of α-adrenoceptors for the modulation of ventromedial hypothalamic pathways that interfere with the regulation of the two cations: stimulation of α₁-adrenoceptors facilitates, while stimulation of adrenoceptors inhibits the excretion of the ions.