We immunostained brain tissues of patients with Alzheimer's disease (AD) together with non-demented aged and younger controls with a battery of anti-human hemopoietic cell monoclonal antibodies (OK series, Ortho Diagnostics Co., Ltd. and some others) by the avidin-biotin-peroxidase complex (ABC) method to see if any epitopes are shared with the nervous system or might contribute to the neurodegenerative changes in this disease. One out of 29 monoclonal antibodies, OKBcALLa, which recognizes common acute lymphocytic leukemia antigen (CALLA, CD10), immunostained senile plaques in the brains of patients with AD. The pattern and intensity of this staining, using cryopreserved samples, was almost identical to that obtained with anti beta-protein. Thus, senile plaques in the Alzheimer's brain share an epitope with CALLA.