Rats given electroconvulsive shock following a one-trial passive avoidance step-down task showed amnesia for that task. Administering adrenocorticotropic hormone, 4 h after training, produced recovery of the avoidance behavior. This suggests that reactivating the internal physiological state present during training is sufficient to retrieve memories that are inaccessible following electroconvulsive shock. Hebb (1949) has suggested that following sensory , input, a neural consolidation process, operating over time, permanen tly fixes the memory trace. Electroconvulsive shock (ECS) produces massive electrical interference, which, if given during the consolidation period, should disrupt the neural activity and thereby prevent the permanent fixation of memory (McGaugh & Herz, 1972). Administering ECS shortly after a one-trial learning experience , then, should result in permanent retrograde amnesia (RA) for that experience (Lewis, 1969).Recently, the permanence of this RA has been questioned Spear, 1973). Lewis, Misanin, and Miller (1968) have shown that with a one-trial passive avoidance task followed by ECS, administering a "reminder" footshock at a later time, eliminates the RA. Miller and Springer (1972) found that the RA could be eliminated with ECS-reminder intervals as long as 336 h.Other experiments have shown that reactivating a consolidated memory and following this reactivation with ECS produces apparent amnesia DeVietti & Holliday, 1972) . The time between training and reactivation was 24 h in these studies, an interval that insures consolidation. These combined studies suggest that ECS may not affect memory storage, but rather may interfere with retrieval mechanisms. Springer and Miller (1972) have shown that, in avoidance learning, the aversive training stimulus and the reminder agent do not have similar physical properties. They used ice-water immersion as the training stimulus and footshock as the recovery agent. Footshock was an ineffective recovery agent, however, when an appetitive task was used . This indicates that footshock does not serve as a universal recovery agent. Klein (1972) has shown that the retention deficit found after an intermediate retention interval with the Kamin effect can be eliminated by administering adrenocorticotropic hormone (ACTH). Klein suggests that ACTH may mediate aversive memories. Levine and *This research was supported in part by a grant from the Graduate Research Council, LSU, to A. G. Young.