To examine the role of monoamines in regulating beta-endorphin levels in discrete brain nuclei, the levels of beta-endorphin-like immunoreactivity (beta-ENDi) were determined in the hypothalamic nuclei of rats 2 h after they were treated with monoaminergic drugs. Sulpiride decreased the levels of beta-ENDi in the nucleus paraventricularis, nucleus arcuatus and median eminence. Domperidone decreased the levels of beta-ENDi in the nucleus aracuatus and median eminence. L-DOPA increased the levels of beta-ENDi in the nucleus anterior hypothalami and median eminence. Phenylephrine or prazosine did not alter the levels of beta-ENDi. Yohimine decreased the levels of beta-ENDI in the nucleus anterior hypothalami. Isoproterenol increased the levels of beta-ENDi in the nucleus arcuatus, and propranolol reversed this effect. These results suggest that dopamine and noradrenaline (via beta-adrenoceptors) may regulate beta-endorphinergic neurons in the rat hypothalamus.