We previously have shown that 6 h of restraint stress in intact male rhesus macaques (Macaca mulatta) suppresses plasma levels of both LH and testosterone and that this effect lasts beyond the period of restraint. Since corticotropin-releasing hormone (CRH) inhibits both the GnRH pulse generator and LH release in ovariectomized macaques and is generally thought to be the central mediator of stress-induced inhibition of gonadotropin release, we investigated the influence of CRH administration on LH and testosterone in unrestrained intact male rhesus macaques. Blood samples were collected from 5 intact male macaques at 15-min intervals for 15 h from a remote site. During this time, each animal received a 4-h infusion of CRH (100-micrograms bolus followed by 100 micrograms/h for 4 h) through an indwelling jugular catheter. Blood samples were collected for an additional 8 h after cessation of the CRH infusion. ACTH and cortisol levels were significantly elevated during and after the CRH infusion and were comparable to levels observed during restraint. Although LH levels appeared lower in animals given CRH, they were not different from those in untreated control males. In some animals, CRH appeared to stimulate or prolong LH release. Testosterone levels in CRH-treated animals were significantly lower than in controls both during and after CRH administration. In some instances, increases in plasma LH were not accompanied by a rise in testosterone. This would suggest that as was observed in restrained animals, stress exerts either a direct or an indirect inhibition of testicular testosterone secretion. The present data indicate that this effect may be mediated by CRH.