The monoclonal antibody M 35 was used to study the cellular and subcellular distribution of muscarinic acetylcholine receptors in the human cerebral cortex. M35, raised against purified muscarinic receptor protein, exerts muscarinic agonist-like effects at cholinergic synapses. Applied to human cortical tissue immediately fixed upon neurosurgical removal, light microscopically M 35 revealed immunoreactive perikarya predominantly of the pyramidal cell type in layers II/III and V, their labeled apical dendrites extending into the superficial layers. Furthermore, immunoprecipitate decorated distinct regions of the perikaryal cytoplasm, numerous dendritic profiles and synapses of both symmetric and asymmetric appearance. In the perikarya immunoprecipitate was associated with ribosomes, the endoplasmic reticulum and the Golgi apparatus. In dendrites the microtubular system, in synaptic complexes the postsynaptic membranes were decorated. The results suggest that novel informations about the cell type specific and subcellular distribution of human muscarinic cholinoceptors can be obtained by M 35 immunocytochemistry.