Acetylcholinesterase (AChE) histochemical staining occurred in neurons of the dentate gyrus at the day of birth and steadily increased in intensity and distribution during the first 3 postnatal weeks until the adult pattern was reached. Granule cells failed to display AChE staining; however, the somata of most non-principal cells in these regions showed AChE activity. It is interesting that most hilar neurons in the dentate gyrus were AChE-positive, but molecular layer local circuit neurons and pyramidal basket cells associated with the granule cell layer did not display AChE staining. AChE reaction product was localized to the nuclear envelope and cisternae of the granular endoplasmic reticulum in the labeled neuronal somata. In addition, the neuropil in the dentate gyrus displayed AChE staining associated with membranes. The possible cholinoceptive role of the AChE somata in the hilus is discussed.