Tau is an axonal microtubule-associated protein, whose dysfunction causes neurodegenerative diseases such as Alzheimer's disease and other tauopathies. Earlier studies have shown the interactions of tau with glycogen synthase kinase-3beta, 14-3-3zeta, protein phosphatase 1 and protein phosphatase 2A. In this study, we compared the amounts of these tau-interacting proteins in brain microtubule-enriched fractions from wild-type and tau-deficient mice. Contrary to our expectation, we detected no difference in the amount of these proteins between wild-type and tau-deficient mice. Our findings indicate that only a small portion of tau-interacting proteins are bound to tau in vivo, and suggest the existence of other scaffolding proteins. We propose that tau-deficient mice are an ideal system for confirming the function of tau-interacting proteins.