Acetylcholinesterase-containing neurons were investigated in primary cultures of cerebral cortex. Neuronal cholinesterase staining was essentially totally attributable to acetylcholinesterase based on its pattern of sensitivity to pharmacological inhibitors. The mean percentage of stained neurons in the cultures was 2.17. Stained neurons of all morphologies were detected: however, the majority of the cells possessed bipolar morphology. The stained bipolar neurons were not a homogeneous morphological population.