• Choline acetyltransferase and acetylcholinesterase activities as well as serotonin and imipramine binding were determined in the hypothalamus, nucleus basalis of Meynert, and frontal and temporal poles of subjects with Pick's disease. Choline acetyltransferase activity was decreased in the hypothalamus and nucleus basalis of Meynert, and acetylcholinesterase activity was decreased in the nucleus basalis of Meynert only. Serotonin binding was decreased in all sites but the nucleus basalis of Meynert, and imipramine binding was altered only in the frontal pole. Comparison with previous reports of Alzheimer's disease indicates that with respect to these synaptic markers, Alzheimer's disease and Pick's disease are not similar.