The effect of β-endorphin on hypothalamic dopamine metabolism was examined in male rats. Intracisternal administration of synthetic human β-endorphin (15 μg blunted the α-methyltyrosine-induced decline in the concentration of hypothalamic dopamine. Also, β-endorphin blunted the pargyline-induced accumulation of hypothalamic dopamine. β-Endorphin either increased or failed to alter the basal concentration of hypothalamic dopamine and failed to alter the basal hypothalamic concentration of the dopamine metabolite, homovanillic acid. These data suggest that β-endorphin decreases the turnover rate of hypothalamic dopamine and are consistent with the thesis that β-endorphin decreases the release of dopamine from tuberoinfundibular dopamine neurons. (Endocrinology106: 76, 1980)