Western blots of soluble tau isoforms quantified by scanning densitometry. The overall quantities of soluble tau isoforms substantially varied among the different PSEN mutations and SAD cases and from the ND controls. Most of the tau proteins were concentrated between ~60–40 kDa. In general there was more tau protein in the PSEN mutations than in the ND controls. There were prominent bands at ~100–110 kDa in 7 out of 10 PS mutations that were absent in the ND controls. Likewise, this band was seen in 3 out of 4 of the SAD cases and not in the ND controls. These bands may correspond to dimeric forms of tau. SAD = sporadic Alzheimer's disease; ND = non-demented.