Different effects of normal aging on muscarinic and nicotinic receptor subtypes were observed in postmortem brain tissue from different regions of the human brain. A significant decrease in M1 and M2 receptors was found in cerebral cortex, while the M1 and especially the M2 receptors increased with age in the thalamus. A similar pattern of changes was also observed when using (-)3H-nicotine as ligand for nicotinic receptors in the cortex and thalamus. No significant changes in nicotinic receptor binding were observed with age in the cortex or thalamus when using 3H-acetylcholine as ligand. Nicotinic and muscarinic receptors in the brain are not equally affected in dementia disorders. A marked loss of high affinity nicotinic receptors was observed in cortical tissue from patients with Alzheimer's disease and with multi-infarct dementia (MID). The muscarinic receptors were (both M1 and M2) increased in Alzheimer cortical tissue while they were decreased in MID.