The term "Alzheimer's disease" is currently used to refer to senile and also presenile dementia, but the heterogeneity of this disorder is demonstrated in many of its aspects. This is of great theoretical interest, and with the appearance of new therapeutic interventions, it may well also start to have very significant practical importance. To shed some light on the debate, the Fondation Ipsen organized an international symposium which took place on April 6, 1992. This volume contains the proceedings of this meeting, which was attended by researchers in epidemiology, clinical neurology and geriatrics, neuropsychology, neuropathology, molecular biology, and genetics.