Deep tendon reflexes, plantar responses, muscle tone, and release signs were studied as 14 individual clinical variables and as five summary variables in 135 aged subjects, including 27 control subjects, 20 subjects with mild cognitive impairment, and 88 subjects with successive stages of probable Alzheimer's disease. Changes in activity of elicited responses were rated on a seven-point scale. Results were analyzed both as prevalence and mean degree of change in activity. Rating on a variable combining all 14 individual variables was significantly higher in a group with mild cognitive impairment than in a control group. Subjects with an early stage of Alzheimer's disease had both higher prevalence of increased activity and increased mean scores of deep tendon reflexes and muscle tone. They had a higher prevalence of increased activity on a variable combining three release signs. Patients with a late stage of Alzheimer's disease had significantly increased prevalence and mean scores of muscle tone and grasping and sucking reflexes compared with control subjects and patients with the early stage of Alzheimer's disease.