The role of the septohippocampal pathway in working memory was investigated by direct microinfusion of compounds into the medial septal area (MSA). Behavior was measured by performance in a continuous spatial alteration task in a T maze, and hippocampal theta rhythm was also recorded. Intraseptal saline had no effect on choice accuracy or hippocampal theta rhythm. Tetracaine decreased choice accuracy and theta rhythm 10 min, but not 90 min, after infusion. Likewise, muscimol and scopolamine produced a transient, dose-dependent suppression of hippocampal theta rhythm and a simultaneous dose-dependent impairment in choice accuracy. A significant correlation (r = .78) emerged between a compound's influence on theta rhythm and its effect on choice accuracy. The data support a role for the septohippocampal projection in working memory and suggest that gamma-aminobutyric acid and acetylcholine may have opposing influences on neurons in the MSA.