Procedures are described for lesioning two components of the hippocampal formation (hippocampus, subiculum) using multiple injections of small amounts of ibotenic acid (IBO). The resulting loss of cells is more selective and limited than can be obtained with conventional techniques. Thus, problems associated with damage to adjacent areas, fibers-of-passage, and damage to the vasculature are minimized. The results of behavioral experiments indicate that the effects of IBO lesions of the hippocampus are more subtle than those found with conventional lesion techniques. The general approach of using multiple injections of small amounts of neurotoxins can be used to selectively lesion other components of the hippocampal formation.