BACKGROUND/AIMS: The aim of this study was to investigate the diagnostic role of CSF beta amyloid(1-42) levels and auditory event-related potentials (AERPs) in the progression of mild cognitive impairment (MCI) to Alzheimer's disease (AD).METHODS: In fifty three MCI patients a lumbar puncture was performed and beta amyloid(1-42) levels were determined. Twenty patients were re-examined after 11 months. During this period five of them progressed to AD. Neuropsychological and ERP examinations were performed in all patients at both exams.RESULTS: Compared to MCI stable patients, AD-converters showed significantly lower beta-amyloid(1-42) values both for group 1 (Mann Whitney test, Z=-2.952, p=0.003, effect size r=-0.41) and group 2 (Z=-2.458, p=0.011; effect size r=-0.55). On the other hand, the patients of group 1 who converted to AD had prolonged latencies and lower amplitudes of the P300 wave compared to those of the MCI-stable patients, although the differences were not significant.CONCLUSIONS: Compared to the separate use of CSF beta-amyloid(1-42) and AERPs, higher values of sensitivity and specificity were achieved by the combined use of beta-amyloid(1-42) levels and P300 latencies (80% and 98%) or amplitudes (100% and 89%) in the discrimination between AD converters and MCI stable patients. Therefore the combination of an electrophysiological and a biological marker is potentially of high diagnostic value for the early diagnosis of AD converters.