Abstract: In an ex vivo method of differentially diagnosing dementias selected from a group of demetias, which includes vascular dementias and frontotemporal lobe degenerations, a concentration of at least one carboxy-terminally truncated amyloid ? peptide species as a biomarker is determined in a body fluid obtained from a patient, the at least one carboxy-terminally truncated amyloid ? peptide species being selected from the group of species consisting of A?1-38, A?1-37 and A?1-39; and the concentration of the at least one carboxy-terminally truncated amyloid ? peptide species is compared to a threshold concentration value for the respective one carboxy-terminally truncated amyloid ? peptide species.