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Recent work has demonstrated that posttraining systemic opioid antagonist administration facilitates the acquisition of a radial arm maze task in new spatial environments. In this study, we examined the effect of posttraining naloxone and β-endorphin microinjections into the medial septal area on the acquisition of a radial maze task in new spatial environments. The results of these experiments demonstrated that posttraining intraseptal naloxone administration facilitated, whereas posttraining intraseptal β-endorphin administration impaired, the acquisition of criterion performance on a maze task performed in new spatial environments. Further, intraventricular β-endorphin administration did not produce effects that were comparable to those observed following intraseptal β-endorphin administration, which indicates that the septal region is a brain site that is sensitive to the effects of opioids on spatial memory in new environments. Further, posttraining intraseptal β-endorphin administration had no effect on working memory in a familiar spatial environment, whereas pretraining intraseptal β-endorphin administration had no effect on the performance of a previously acquired spatial task.