The storage pigment in neuronal ceroid lipofuscinoses (NCL) has a close similarity to age pigment lipofuscin. We studied immunoreactivity of isolated neuronal pigments from the juvenile form of NCL and aging control, using monoclonal antibodies (mAbs) against amyloid beta-protein. Ultrastructural localization of the immunoreactivity demonstrated that in NCL the epitopes are distributed mainly in curvilinear multilamellar arrays of the storage pigments and less in fingerprint profiles, while in aging control they are more homogeneously distributed on age pigment lipofuscin. The different distribution of the epitopes may reflect some catabolic as well as morphologic differences in lysosomes. A unique 31-kDa polypeptide detected on Western blots in NCL possibly derives from the same precursor, amyloid beta-protein precursor (ABPP). ABPP processing may be aberrant in NCL brains, and this can be detected as a 31-kDa polypeptide reactive with the mAbs.