• The performances of 89 patients with dementia of the Alzheimer type (DAT) and 53 demographically matched elderly normal control subjects were compared on four verbal fluency measures (category, letter, first names, and supermarket fluency). Receiver operating characteristic curves were plotted to determine each fluency tasks' sensitivity (ie, true-positive rate) and specificity (ie, true-negative rate). Category fluency demonstrated the greatest degree of discrimination between patients with DAT and normal control subjects (sensitivity, 100%; specificity, 92.5%); letter fluency was the least accurate (sensitivity, 89%; specificity, 85%). Separation of patients with DAT by gender revealed similar findings. In further analyses with a subgroup of 21 mildly impaired patients with DAT, category fluency lost none of its discriminative capabilities, whereas all other fluency measures showed marked reductions in discriminability. We conclude that this superiority of category fluency is due to its dependence on the structure of semantic knowledge, which deteriorates in the early stages of DAT.