The computed tomograms (CTs) of 13 mild to moderately impaired patients with senile dementia of the Alzheimer's type (aged 65 to 82 years) were compared with CTs of 18 healthy age-matched controls. Two computer programs and a variety of linear measurements were used to analyze the CTs. A measure of the mean CT density number of the brain tissue on the slice at the maximum width of the bodies of the lateral ventricles correctly predicts the group membership of 77.42% of the subjects. The addition of a second computerized variable, the fluid volume on the slice at the maximum width of the third ventricle, increased discriminating power to 93.55%. The CT density numbers may provide highly valuable information for the diagnosis of Alzheimer's disease in the senile age range.