The present invention provides an ex vivo method for aiding the diagnosis of Alzheimer's disease in a patient, the method comprising the steps of determining the level of expression of at least four platelet proteins in a platelet sample from the patient selected from monoamine oxidase-B, coagulation factor Xllla, total tropomyosin (a and 13), WD-repeat protein 1 and apolipoprotein E4; and comparing the result of (i) to a control value, wherein a result higher than the control value is indicative of Alzheimer's disease. Preferably, the method of the invention further comprises determining the level of expression of wild-type GSTO-1 or mutant GSTO-1.