Tau accumulating as paired helical filaments (PHF) in Alzheimer's disease brain is considered to be abnormally phosphorylated on distinct sites. To compare the phosphorylation state of tau-positive neuronal inclusions among diverse neurologic diseases, we have probed these lesions with three well-defined PHF/tau monoclonals, C5, M4 and tau 1, that most likely recognize three proline-directed phosphorylation sites in PHF-tau. In Alzheimer's disease brain all three monoclonals intensely immunostained intracellular neurofibrillary tangles, neuropil threads, senile plaque neurites, and "pretangle neurons" in a phosphorylation-dependent manner. They also stained, in the same manner, Pick bodies in Pick's disease, and neurofibrillary tangles and neuropil threads in various tangle-forming neurologic diseases. In most of these diseases (including Pick's disease, progressive supranuclear palsy, subacute sclerosing panencephalitis, and Alzheimer's disease) astrocytes and oligodendrocytes were found to contain tau-positive inclusions which showed the same immunocytochemical characteristics. Thus, the widely occurring tau-positive inclusions share common phosphorylation characteristics irrespective of underlying diseases or cell types.