Neurons of the medial septum-nucleus of the diagonal band of Broca (vertical limb) area were identified as septo-hippocampal neurons by antidromic electrical activation in anesthetized rats. A large majority of these presumably cholinergic neurons could be excited by the iontophoretic application of acetylcholine or cholinergic agonists such as carbachol. The acetylcholine-induced excitations were readily antagonized by atropine. These results suggest that cholinergic neurons can be excited by their own transmitter, i.e. acetylcholine.