Place learning and memory were assessed in rats with selective damage to the fornix/fimbria or to subcortical structures which have a major connection with the hippocampal formation via the fornix/fimbria. Navigation to a hidden or visible platform in a fixed location was studied in the Morris water task in rats who were preoperatively trained in the task or who were preoperatively naive. All rats learned to navigate accurately to a visible platform. Only complete transection of the fornix/fimbria abolished both acquisition and retention of navigation to a hidden platform. Severe impairment of postoperative acquisition was produced by bilateral damage to the medial nucleus accumbens or bilateral damage to the anterior thalamic area. Nucleus accumbens or anterior thalamic damage produced little effect on retention of preoperatively acquired place navigation. Damage to medial septum or mammillary complex produced modest impairments evident only in postoperative acquisition.