The nervous-system-specific microtubule-associated Tau proteins promote microtubule stability and assembly. Tau is transiently phosphorylated at about 30 positions and additionally O- and N-glycosylated. Bovine Tau was prepared from a calf brain and purified by affinity chromatography using immobilized monoclonal antibody (mAb) BT-2, which recognizes all Tau-splicing isoforms. Tau was obtained in high purities well above 90% containing even highly phosphorylated Tau versions with isoelectric points below pH 5 without discrimination. Moreover, these highly phosphorylated versions were detected only after purification. The purification progress and the final purity were studied by two-dimensional gel electrophoresis (2DE) using both protein and phosphoprotein stains as well as immunoblots. (c) 2006 Elsevier Inc. All rights reserved.