This paper presents a study to test the hypothesis that a parkinsonian subtype of Alzheimer's disease exists. Twenty-one patients with dementia of the Alzheimer's type (DAT) and coexistent parkinsonian features were matched to 21 DAT control patients without parkinsonian signs. All subjects were drawn from 136 patients with DAT evaluated between 1980 and 1982. Items from a standardized clinical evaluation at the time of diagnosis, from continuous yearly follow-ups, and neuropathologic examination were compared to determine if qualitative differences exist between the two groups. Those with parkinsonian features had significantly shorter duration of symptoms prior to presentation, a trend toward more reports of decreased self-care, and more primitive reflexes on physical examination. While the total Folstein Mini-Mental State Exam (MMSE) scores at presentation were not significantly different, the cases showed greater impairment in language and registration subitems. During follow-up, no differences were observed in performance on MMSE and Dementia Rating Scale scores. Survival curves showed a trend toward poorer survival in the cases. Neuropathologic data were obtained on seven patients with both DAT and parkinsonian features and showed three cases with Alzheimer's disease (AD) alone and four with AD and Parkinson's disease. Four of the DAT control patients were examined neuropathologically, and all had AD without evidence of Parkinson's disease. The results provide preliminary evidence that Alzheimer's patients with parkinsonian signs are a subtype characterized by distinct neurologic signs and a more rapid course.