To test the effect of opiate receptor blockade on hormone release in man, we administered 10 mg naloxone iv to eight normal subjects and compared the results with those found after saline infusion. Naloxone produced a rise in serum cortisol (P < 0.01), LH (P < 0.01), FSH (P < 0.05), and insulin (P < 0.05) levels but did not alter serum GH, PRL, TSH, arginine vasopressin, glucagon, T3, or T4. Naloxon e had no effect on GH levels in two subjects with active acromegaly or on TSH levels i n six subjects with primary hypothyroidism. In dynamic pituitary function testing, naloxone diminished the GH response to arginine (P < 0.05) without altering the PRL response; naloxone augmented the PRL response to TRH (P < 0.025) without affecting the TSH response. Naloxone did not significantly alter GH or PRL response to L-dopa. Naloxone enhanced the increment in serum cortisol induced by the stress of gastroscopy without changing the GH or PRL response. Naloxone increased glucose response areas (P < 0.05) after an iv gl...