A monoclonal antibody to the nerve growth factor receptor (NGFR) (IgG 192) was used to visualize differences in immunohistochemical labeling of young (10 months) and old (35 months) rats. Three parameters were analyzed; cell counts, immunoreactive cross-sectional surface area (SA) and optical density (OD) of labeled cells. Large reductions in all three parameters were recorded in the medial septum (MS). Both OD and immunoreactive SA were reduced in the VDB, while only OD was reduced in the HDB. This observation confirms that NGFR labeling is reduced in the aged rat septum and adds that the loss of labeling is differential, with greater deficits in the MS-VDB complex than in the HDB.