Two double-blind, placebo-controlled cross-over studies were conducted to evaluate the effects of naltrexone hydrochloride, an oral opiate antagonist, on adrenergically-mediated cardiovascular responses in older and younger, Black and White normotensives and hypertensives with varying lengths of hypertension duration. Cardiovascular and opioid responses were measured in response to a stressor combined with either placebo or naltrexone pretreatment. Results from these studies assisted in (a) elucidating opioidergic mechanisms underlying the increased rates of hypertension morbidity and mortality among Blacks and the elderly, and (b) ultimately optimized the design of pharmacological interventions for the prevention and treatment of hypertension.