This study describes the colocalization of muscarinic acetylcholine receptors (mAChRs) and the neuropeptide somatostatin (SOM) in nonpyramidal neurons of the rat dorsal hippocampus. SOM and mAChRs were identified by immunocytochemistry employing antibody S309 and M35, respectively. Half of the SOMergic cell population is found to be immunoreactive for muscarinic receptor protein as obtained by fluorescent double-labeling techniques. These findings provide additional evidence for a direct cholinergic influence upon SOMergic, nonpyramidal neurons, and defines the anatomical distribution of SOMergic, cholinoceptive neurons in the dorsal hippocampus. Concerning the muscarinic cholinoceptive, nonpyramidal neuron population of the dorsal hippocampus, a considerable number (approximately one-third) was found to be colocalized with somatostatin. These results indicate that a significant part of the cholinergic influence upon hippocampal nonpyramidal neurons is relayed via SOMergic neurons.