Using immunofluorescence histochemistry, in the human cerebral cortex neurons immunoreactive for both nicotinic and muscarinic acetylcholine receptor proteins could be demonstrated. Vibratome sections of biopsy and autopsy specimens of human temporal and occipital lobes were incubated with monoclonal antibodies specific for muscarinic (M 35) and nicotinic (WF 6) acetylcholine receptor protein. Immunoreactive sites were visualized using a biotin-streptavidin-phycoerythrin system (M 35, red fluorescence) and fluorescein-conjugated immunoglobulins (WF 6, green fluorescence). Immunofluorescence of both antibodies was preponderant in pyramidal neurons located in layers II/III and V and their apical dendrites. Some round and ovoid immunolabeled cells were encountered in layers VI and IV. About 30% of the cholinoceptive cortical neurons, in particular the pyramidal cells, displayed immunoreactivity for both receptor types. The present investigation shows a subpopulation of human cortical neurons to contain both nicotinic and muscarinic receptors. The coexistence of acetylcholine receptors may provide the morphological basis of simultaneous impact of acetylcholine on both receptor types in the same neuron of the human cerebral cortex.