The categoric verbal fluency (colors, animals, fruits and cities) was prospectively evaluated with the set-test in a group of 71 patients with dementia (Alzheimer's disease 38, vascular dementia 19, mixed dementia 2, other dementias 12). In all types of dementia, greater decreases in the categoric verbal fluency were found with greater degrees of severity. However, for equal degree of deterioration, patients with Alzheimer's disease had the smallest scores in the set-test as compared with other types of dementia. 90% of the percentile distribution of patients with Alzheimer's disease had set-test scores below 25. The hypothesis that a set-test score lower than 25 is diagnostic for Alzheimer's disease has a 87% sensitivity and a 67% specificity. It is concluded that in patients with criteria of probable Alzheimer's disease a set-test score lower than 25 supports the diagnosis.