8 mg of naloxone were administered IV to 14 normal volunteers in a placebo-controlled, double-blind experiment. Plasma levels of beta-endorphin, cortisol, prolactin, growth hormone, HVA and MHPG were determined before and 45 min after administration. Naloxone elicited significant increases in cortisol and MHPG but did not change plasma levels of the other compounds. In an additional experiment on two subjects, 20 mg of naloxone caused elevations of beta-endorphin as well as of cortisol. This parallel increase indicates that the linkage between the secretion of beta-endorphin and ACTH/cortisol may be dose-dependent. The increase in MHPG is in agreement with the hypothesized association of noradrenergic hyperactivity and opiate withdrawal.