There is an urgent need for biomarker-based tests that enable a more accurate and early diagnosis of Alzheimer disease (AD).Recently it has been shown that CSF levels of β-amyloid (Aβ) peptides and t-tau define a biomarker signature that allow identification of mild AD and appears to predict conversion from mild cognitive impairment to AD.Indirectly these results reinforce the idea that A β levels in blood could also have diagnostic significance though many questions regarding procedence and metabolism of the circulating Aβ remain to be clarified.Attempts to measure Aβ peptides in blood and to use them as disease biomarkers have given inconclusive and discouraging results until now; mostly by a variety of technical reasons that certainly compromise,but do not invalidate,the working hypothesis.We have developed two ELISA kits (ABtest40 and ABtest42) that allow the direct determination of the β-amyloid pool in blood by the quantification of both Aβx-40 and Aβx-42 free in plasma,bound to plasma proteins and bound to the blood cells.Our current work was aimed to obtain preliminary "translational" data after moving our kit from basic research to discriminate between mild cognitive impairment (MCI),AD patients and healthy controls.