Quantitative autoradiography was used to determine the density and distribution of [3H]1-[1-(2-thienyl)-cyclohexyl]piperidine ([3H]TCP) binding sites in human hippocampal tissue sections from control and Alzheimer's disease patients. Some Alzheimer's cases showed no changes in binding site density while other cases showed substantial declines in the CA1 region. [3H]TCP binding in the CA1 region from Alzheimer's patients was reduced an average of 40% while the other hippocampal regions were unaffected. It is proposed that the loss of [3H]TCP sites in the hippocampal CA1 region of certain Alzheimer's cases is associated with the greater cell loss observed in cases of severe Alzheimer's disease.