We studied the immunocytochemical distribution of amyloid beta/A 4 protein precursor (APP) in both the central and peripheral nervous tissues of the mouse. We used two different antisera against the synthetic peptides corresponding to the carboxyl- and the amino-terminal regions of APP, which are common to all isoforms of APP (APP695, APP714, APP751 and APP770). Both antisera recognized the same 106-122 kDa proteins from the mouse brain on immunoblotting. Immunocytochemically, in cortical and subcortical areas, reactivities of both antisera were located in neurons of all sizes. Immunoreactive neurons were widely distributed showing no particular pattern. Various neuron types in the spinal cord were also immunoreactive. In the peripheral nervous system, ganglion cells and their processes showed immunostaining. Immunoreactivity was also seen in the astrocytes, oligodendroglia and ependymal cells widely distributed in the brain and spinal cord, mantle cells in the ganglia, and Schwann cells in peripheral nerves. These results indicated that the full length of APP is distributed in almost all neurons and some glial cells in the mouse central and peripheral nervous systems.