The status of cholinergic receptors in dementia is related to the question of potential cholinergic therapy. Whilst muscarinic receptor binding is generally reported to be normal or near normal, findings are reported which indicate substantial reductions of hippocampal nicotinic (high affinity nicotine) binding (occurring in conjunction with decreased choline acetyltransferase) in both Alzheimer's and Parkinson's but not Huntington's disease. A further indication that nicotinic receptor function may be abnormal in Alzheimer's disease is the extensive loss of an endogenous compound, detected for the first time in human brain, which inhibits normal nicotinic binding. Both receptor binding and the inhibitor are also substantially decreased with increasing age in the normal hippocampus.