Choline acetyltransferase and acetylcholinesterase have been assessed in human aging brains, in demented and agonal states. Choline acetyl transferase decreased during aging in normal brain when measured in the cerebral cortex. Choline acetyltransferase was also reduced in several other brain areas in patients with Alzheimer's disease and in one patient with Creutzfeldt-Jakob disease. Choline acetyltransferase was also reduced in bronchopneumonia and in some terminal conditions. On the contrary, the activity was not reduced in patients who died after cerebrovascular accidents. Acetylcholine esterase, although it followed the general trend of choline acetyltransferase, did not yield significant results.