Substance P-like immunoreactivity was visualized by immunohistochemical methods in 20 postmortem brains: 6 senile, 4 presenile Alzheimer dementia (AD), 3 AD with interhemispheric asymmetric cortical atrophy, and 7 control cases. For all pathological cases, the SP-like immunoreactivity was significantly reduced in the neocortical areas and in the hippocampus. This contrasted with an enhanced SP-like immunoreactivity in the pallidum and the substantia nigra in AD brains and a more pronounced SP-like immunoreactivity in the more atrophic side in the asymmetrically atrophied brains.