Rats were tested in a new spatial discrimination procedure which measured working memory. Following preoperative testing, lesions were placed to disrupt each of the major extrinsic fiber connections of the hippocampal formation. Destruction of the entorhinal area, body of the fimbria-fornix anterior to hippocampus, septum, or postcommisural fornix produced a severe and consistent impairment in performance. Analysis of error patterns indicated that when animals with limbic lesions made errors, they were likely to make these errors in the same sequence as the original choices. These data support the hypothesis that the hippocampus has an important role in the processing of information about spatial location, and that normal performance on this task requires an intact hippocampal circuitry.