The learned taste aversion paradigm was employed to test for aversive effects of microinjections of carbachol to the medial septum, lateral ventricle and ventral hippocampus. To determine the locus of action of carbachol, either a central cholinergic blocker (atropine sulfate) or a peripheral cholinergic blocker (atropine methyl nitrate) was administered concomitantly with carbachol. Carbachol administered to the medial septum resulted in a learned taste aversion that was mediated by central cholinergic systems. Administrations to the lateral ventricle resulted in a learned taste aversion mediated by a peripheral cholinergic effect. Administrations to the ventral hippocampus did not result in a learned taste aversion but appeared to condition an aversion to being handled. It is concluded that centrally administered carbachol produces an altered internal state which is aversive to the animal, and the mechanism underlying this phenomenon is dependent upon the site of administration. © 1977.