Administration of the opiate receptor antagonist, naloxone, evoked rapid rises in plasma LH levels in estrogen, progesterone-primed ovariectomized rats. Pretreatment with a peripherally acting epinephrine (EPI) synthesis inhibitor, SK&F 29661, failed to influence the naloxone-induced LH release. However, two centrally acting EPI synthesis inhibitors, SK&F 64139 and LY 78335, which selectively suppressed hypothalamic EPI levels, blocked stimulation of LH release by naloxone. These results implicate brain EPI neurons in mediation of endogenous opioid peptide influence on LH release.