During the reproduction of a conditioned passive avoidance response by albino rats and also during the action of a conditioning stimulus in animals trained by invariable reinforcement of the conditioning stimulus, a significant decrease was found in the noradrenalin content in nuclei of the limbic system and anterior hypothalamus compared with the control. In untrained animals, and also in trained animals subjected to repeated testing in the course of 4 days, the decrease in the noradrenalin content was less marked. Reproduction of the conditioned active avoidence response in a shuttle box did not induce changes in the noradrenalin content.