Neuropathological studies of 10 confirmed cases of Alzheimer's disease (AD) revealed increased numbers of neurofibrillary tangles and neuritic plaques in olfactory cortex compared to other brain regions. This was most evident when AD tissues were compared to tissues from seven gender- and age-matched controls. In the AD cases, examination of other brain regions which receive olfactory projections also revealed high concentrations of neuritic plaques and neurofibrillary tangles. These data also confirm previous observations that neurofibrillary tangle formation is more prevalent than neuritic plaque formation in AD. This is the first quantitative neuropathological study that demonstrates significant damage to various components of the central olfactory apparatus in AD. Our data suggest that damage to these areas may be related to the behavioral, emotional, and cognitive abnormalities commonly observed in affected patients. The use of antemortem evaluation of the olfactory system as a diagnostic tool for AD is discussed.