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Normal male rats were subjected to a variety of stress stimuliincluding simple handling, transfer from room to room, ether anesthesia alone or combined with bleeding, the injection of saline or epinephrine, and restraint. The ensuing secretory responses of prolactin, LH, GH and FSH were then determined. Although the secretion of all 4 hormones is affected by stress and their secretory responses have a nonspecific character, they differ both in susceptibility and reactivity to stress stimulation. The secretions of prolactin and GH are the most susceptible, and whereas the secretion of prolactin is enhanced, the secretion of GH is inhibited. The secretion of LH is less susceptible and the secretory responses are more complex: an initial stimulatory phase is often followed by an inhibitory phase. The secretion of FSH is the least susceptible, but when a secretory response is elicited, it is paralleled by the secretory change in LH.