Abstract: Described is a method for the diagnosis of Alzheimer's disease (AD) or a particular stage of the disease which is based on the determination of the ratio of at least two gamma-secretase cleavage products, Abeta48, Abeta45, Abeta42, Abeta38 and Abeta35, preferably the ratio of Abeta38: Abeta42. A decreased ratio of Abeta38: Abeta42 as compared to the normal ratio is indicative of AD. Moreover, kits suitable for carrying out said diagnostic method are described.