Using the tritiated ligand [3H]quinuclidinyl benzilate ([3H]QNB), a specific muscarinic cholinergic antagonist, the distribution of muscarinic receptors was determined in 75 specific brain regions and nuclei removed by microdissection as well as in large brain areas. [3H]QNB binding was highest in the caudate-putamen; other regions with high binding included the nucleus accumbens, cerebral cortex and hippocampus, certain limbic and thalamic nuclei, superior colliculus, pontine nuclei and the hypoglossal nucleus. Muscarinic cholinergic receptors may be concentrated in these regions. [3H]QNB binding generally correlated well with acetylcholinesterase staining in terminals and is consistent with certain sites as particularly enriched in cholinergic synapses.