Alzheimer disease is a progressive neurodegenerative disorder that is characterized by a loss of cognitive and memory functions. Amyloid fibrils deposited in neuritic plaque is mainly β-amyloid protein (Aβ) that is derived from amyloid precursor protein (APP). The secreted form of APP, which is corresponded to N-terminal portion of APP, shows neurotrophic activities. On the other hand, Aβ and cytoplasmic domains of APP are thought to be neurotoxic. In order to investigate the effect of C-terminal fragment of APP covering Aβ and the cytoplasmic domain upon cell growth and differentiation, we established a stably transfected cell line producing the C-terminal 100 amino acid pep-tide of APP. The transfected clones stained positively with anti-Aβ monoclonal antibody, TB-1. The growth rate of the transfected cells was not significantly different from that of mock-transfected cells or native NB39 cells. After treatment with all-trans retinoic acid (ATRA), mock-transfected cells extended neurite processes and showed neuronal-like differentiation, while a transfected clone overexpressing C-terminal fragment did not present neuronal-like morphology. These results suggest that ATRA-induced neurite extension may be suppressed by overexpression of the C-terminal fragment of APP.