The stress-induced release of ACTH is believed to involve the activation of several humoral and neural pathways, including corticotropin-releasing factor (CRF), catecholamines and vasopressin. The essential role of CRF was supported by our observation that immunoneutralization of this releasing factor significantly lowers plasma ACTH levels of ether-stressed rats. However, the presence of a small but measurable residual ACTH secretion suggested the possible involvement of factors other than CRF in the stress response. We report here that pretreatment with a vasopressin antagonist decreases the plasma ACTH levels of ether-stressed rats in later (10-20 min), but not earlier (0-10 min), phases of ether stress. The ganglionic blocker chlorisondamine, inhibits ACTH release during both phases of the response to ether by 40-60% when used alone, and by 100% when administered with anti-CRF antibody. These results support a role of CRF, catecholamines and vasopressin in mediating ACTH release by ether stress.