The purpose of this study was to examine the utility of the clock drawing task (CDT) in differentiating between patients with mild and very mild Alzheimer's disease (AD) and normal controls. Thirty normal elderly individuals and 30 patients with probable AD were entered into the study and asked, in a standard fashion, to draw a clock from memory. All the clocks were scored according to two previously described standardized scoring systems, and the accuracy of classification into normal or AD groups was determined. Both CDT scales could discriminate between moderate AD and normal aging but lacked sensitivity in the very mild AD cases; mild cases showed intermediate sensitivity. In conclusion, the CDT as a test for AD is insensitive in the early-stage cases, but sensitivity improves with increasing severity of dementia. The CDT is unlikely to be useful in distinguishing between AD in its early stages and normal aging.