Progress in treating Alzheimer's disease will rest almost as much on the development of an effective and inexpensive diagnostic as it will on the therapeutics themselves. Ideally, a diagnostic would allow distinguishing AD from other dementias and allow detection of the disease before the onset of symptoms. If well people are going to use the diagnostic regularly it must also be inexpensive. We have invented a simple technology -- immunosignaturing -- that may be useful toward these goals. It allows the display of the complexity of antibodies in an individual. If AD produces changes in the immune system and we can read it on these arrays we have developed, it could offer a new and simple way to diagnose AD.