Posttraining administration of the opioid peptides, beta-endorphin or the enkephalins, is known to cause retrograde amnesia for a variety of tasks in rats. The present paper studies the effect of the posttraining administration of dynorphin 1-13 on retention of a step-down inhibitory avoidance task and of a shuttle avoidance task. For the purpose of comparison, the effect of human beta-endorphin was also studied. In confirmation of previous results, beta-endorphin (1.0 or 10.0 micrograms/kg, IP) caused retrograde amnesia for the two tasks. Dynorphin 1-13 had no effect at doses between 0.008-125.0 micrograms/kg IP or 1.25-125.0 ng/rat ICV in the inhibitory avoidance task, or at doses of 5.0, 25.0, or 125.0 micrograms/kg in the shuttle avoidance paradigm. These findings suggest that, in contrast to beta-endorphin, dynorphin 1-13 may not be involved in memory regulation at the posttraining period in rats.