Many patients with dementia of the Alzheimer type (DAT) have an abnormal sense of smell. I studied 18 mildly demented subjects with DAT between the ages of 60 and 80 years and found them less able to identify five fragrances compared with 26 healthy elderly controls. The mean (+/- SEM) olfactory identification score for demented subjects was 0.3 +/- 0.2 compared with 2.8 +/- 0.2 for controls. When the subjects were given a multiple-choice list of ten items including the test fragrances and five other odors, performance of both demented and normal subjects improved, with a score of 1.8 +/- 0.4 for subjects with DAT and 4.2 +/- 0.2 for controls. The findings suggest that olfactory deficits are a sensitive, although non-specific, indicator of mild DAT.