Application of the cholinergic agonist carbachol (50 microM) produced theta-like rhythmical waveforms, recorded in the stratum moleculare of the dentate gyrus. Atropine sulfate (50 microM) antagonized the carbachol-induced theta-like activity, consistent with this action of atropine in vivo. These results provide the first direct evidence that hippocampal neurons are capable of producing synchronized slow-wave activity when isolated from pulsed rhythmic inputs of the medial septum and other brain regions.