The authors have characterized frontal cortical tau protein in cognitively intact (4) and cognitively impaired (ALSci, 4) ALS patients and compared it with control (2) or Alzheimer disease (AD, 1)- derived tau. The authors observed expression of both 3R and 4R tau isoforms; increased insoluble tau protein; phosphatase resistance; and hyperphosphorylation at T175, S208, and S210. Soluble tau from both AD and ALSci was also phosphorylated at S237. Tau hyperphosphorylation is associated with ALS.