The possible effects of subcutaneous administration of dynorphin1-17 on retention of an inhibitory avoidance behavior have been studied in rats. Post-training or pre-test administration of dynorphin1-17 in doses of 25 or 50 micrograms/kg facilitated retention performance in rats subjected to a footshock of 0.2 mA n the acquisition trial. However, the same doses of the opioid peptide exerted a deleterious effect on retention performance when a footshock of 0.4 mA was used after either post-training or pre-test administration. Post-training injection of the kappa-receptor antagonist MR-2266 in doses of 0.5, 1 or 2.5 mg/kg failed to affect retention behavior. However, the previous administration of 2.5 mg/kg of MR-2266 prevented the facilitatory effect exerted by dynorphin1-17 after post-training, as well as after pre-test administration. Our results suggest that dynorphin1-17 may be involved in modulating the consolidation, as well as the retrieval, of recently acquired information.