The synaptic junction from three autopsy cases of adults with Down's syndrome and Alzhemer-type dementia was examined ultracytochemically, using the ethanolic phosphotungustic acid (E-PTA) method. A noteworthy finding was the presence of variable shaped vesicles which were not observed in the ordinary E-PTA-treatcd preparations. Many of these vesicles displayed a wide variety of abnormal shapes between the presynaptic dense projections. Such a change has escaped detection in the E-PTA-treated preparation so far. The presynaptic terminal was considered to be one of the central regions for observing pathological changes, associated with Alzheimer's disease. In addition, the possibility is raised that the qualitative analysis of synaptic junctions, using the E-PTA method, facilitates the acquisition of further information concerning synaptic changes.