Young adult and elderly male and female intact rats, as well as chronically ovariectomized (OVX) young and elderly female rats, were subjected to an acute stress by cutting the tip of the tail and prolactin (Prl) concentrations were measured in their blood collected by decapitation at various times thereafter. Maximum concentrations of the hormone were markedly lower in all the three groups of elderly rats than those found in the corresponding young animals, and appeared to occur with a delay in the females, but not in the males. In addition, the Prl-response to stress was attenuated in OVX animals regardless of their age. The result of these experiments, performed at two points on the age scale, suggests that in sexually mature rats of both sexes the stress-induced secretion of Prl is inversely related to the age of the animal and that the reverse relationship is retained in OVX females.