Endogenous opioid regulation of blood pressure is altered during stress in young adults at risk for hypertension. We studied the effects of the opioid antagonist naloxone on the secretion of corticotropin and B-endorphin during psychological stress in young adults with mildly elevated casual arterial pressures. Naloxone-induced secretion of both corticotropin and B-endorphin was significantly diminished in persons at risk for hypertension compared with the low blood pressure control group. Results suggest that opioidergic inihibition of anterior pituitary function is altered in hypertension development.