The authors used the Hamilton Rating Scale for Depression and a rating of depressed mood to investigate the prevalence of depression in 55 patients with Alzheimer's disease, 37 patients with multi-infarct dementia, and 30 nondemented comparison subjects. The prevalence of depressed mood depended on the severity of dementia as measured by the Mini-Mental State examination and was significantly lower among patients in more severe stages of Alzheimer's disease but not among patients with severe multi-infarct dementia.