Galanin, a peptide of 29 amino acids, is co-localized with acetylcholine in a subpopulation of neurons of the medial septal area (MSA) that project to the hippocampus. Galanin reverses the actions of acetylcholine in several biochemical and behavioral procedures, and may be involved in memory processes. To test the possibility that galanin acts on the cell bodies of MSA neurons, two measures of septohippocampal function were assessed following intra-septal microinfusion of galanin or two synthetic fragments of galanin (1-16 and 21-29). The behavioral measure was choice accuracy in a working memory task in a T-maze. The electrophysiological measure was hippocampal theta activity recorded from the dentate hilus. The galanin fragment, 1-16, and the complete peptide, 1-29, decreased choice accuracy and decreased hippocampal theta activity in a dose-dependent fashion. Saline and the 21-29 fragment had no effect on choice accuracy and hippocampal theta. Sensorimotor performance was unaffected. These findings demonstrate that galanin impairs working memory when administered directly into the MSA and suggest that galanin inhibits MSA neural activity.