The processing of Alzheimer's amyloid precursor protein was studied by Western blotting during H2O2 induced apoptosis in cultures of human neuroblastoma cells. A new 5.5 kDa fragment putatively containing intact A beta was detected and found to be highly associated with apoptosis. The results suggest a possible vicious cycle involving H2O2, A beta and apoptosis which may contribute to the neuronal death mechanism in Alzheimer's Disease.