The type and cell size of parvalbumin-immunoreactive (PV-Ir) neurones were examined in 14 postmortem brains from elderly control and Alzheimer-type dementia (ATD) patients with the aid of an image analyser. Morphological features of PV-Ir neurones suggested the existence of PV in the non-pyramidal interneurones in the cerebral cortex. A significant loss of PV-Ir cells was found in the frontal and temporal cortex in ATD. A significant reduction in the size of PV-Ir cells was also noted in the temporal cortex in ATD. These findings suggested that PV-Ir neurones in the cortex are affected in ATD.