The main aim of the current study was to simultaneously quantify the plasma concentrations of six different phosphorylated tau (p-tau181, p-tau199, p-tau202, p-tau205, p-tau217 and p-tau231) and two non-phosphorylated tau peptides using a targeted MS method to investigate their relationship with AD pathology at different stages of disease development. Here, MAPT is linked to Alzheimer disease.