Neurotransmitters including acetylcholine, dopamine, norepinephrine, serotonin, GABA and vasopressin were examined in control subjects and patients with Alzheimer-type dementia, involving presenile and senile dementia. Neurotransmitters exhibited various mode of changes with aging. Abnormalities found in senile or presenile dementia were not always parallel to the age-related changes. These results suggest that Alzheimer-type dementia cannot be understood as an accelerated senescence, but other etiological factors might be introduced for the manifestation of the dementia. Moreover, the disturbance in neurotransmitters revealed a difference between presenile Alzheimer's disease and senile dementia, indicating that further studies should be carried out taking the age of onset into consideration.