  Given the particle content of the standard model without and with a
right-handed neutrino, the requirement that all anomalies cancel singles out a
set of possible global symmetries which can be gauged. I review this topic and
propose a new gauge symmetry B - 3L_tau in the context of the minimal standard
model consisting of the usual three families of quarks and leptons plus just
one nu_R. The many interesting phenomenological consequences of this hypothesis
are briefly discussed.
