In this work, we investigated the role of serum BACE1 activity as biomarker for AD, estimating the diagnostic accuracy of the assay and assessing the correlation of BACE1 activity with levels of Aβ1 - 40, Aβ1 - 42, and Aβ40/42 ratio in serum, known biomarkers of brain amyloidosis. The gene discussed is BACE1; the disease is Alzheimer disease.