The expression of amyloid precursor protein (APP) in olfactory neuroblasts has been examined with a panel of antibodies directed against varied regions of the APP molecule. The pattern of reactivity was compared to that in the transformed human glial cell line SVG, human cortical brain tissue, and in kidney epithelial 293 cells containing stably transfected and overexpressed human APP751. Antibodies directed against the C-terminus and extracellular domains of amyloid precursor protein (APP) react more strongly on immunoblot with transfected 293 cells and brain tissue than with olfactory neuroblasts (ON) or SVG cells. Antibodies directed against the beta/A4 region of APP show a contrasting pattern of reactivity, yielding greater reactivity with ON and SVG cells than with transfected 293 cells or brain tissue. Analysis of the APP transcripts using polymerase chain reaction indicates that ON and SVG both make predominantly APP770 and 751, as does the transfected 293 cell line. In the absence of any differences in APP transcripts among the cell lines, the difference in availability of the beta/A4 region appears likely to be due to posttranslational modification. These data therefore indicate that processing of APP varies among cell lines and thus may vary from tissue to tissue.