The present study investigated differences between normal elderly subjects matched for age and education and patients with dementia of the Alzheimer's type (DAT) on two measures of reaction time (RT). Statistically significant group differences clearly demonstrate that normal elderly subjects have faster RT than subjects with senile dementia on all RT tasks. The DAT patients were most clearly differentiated in terms of overall group means and clinical classification from their age-matched counterparts on the choice of RT task. Eleven of 12 (92%) DAT patients displayed choice RT's 2 or more standard deviations above those of age-matched normals. While both RT measures were discriminative between patients and normals, the overall results argue for increased sensitivity when choice is required in RT in accessing the cognitive deficits in DAT.