A monoclonal antibody against the muscarinic acetylcholine receptor was used to study the distribution of this receptor within the cat visual cortex at the light and electron microscopic level. Immunolabelling was found to be distributed mainly in cell bodies and dendrites in both young and adult cats. The laminar distribution, however, changed during development from cortical layers IV and to a lesser extent II in kittens of 28-42 days of age into one favouring the upper (L I-III) and lower layers (L V and VI) in kittens and cats more then 60 days of age. Electronmicroscopy revealed staining of membranes of cell bodies and dendrites and a great amount of intra-cellular staining of vesicles and internal membranes. Since the receptors are found on cell bodies and dendrites in both kittens and adults this indicates that different populations of cortical cells express these muscarinic receptors at different postnatal ages.