  We overview the constraints on the 4th-generation neutrino dark matter
candidate and investigate a possible way to make it a viable dark matter
candidate. Given the LEP constraints tell us that the 4th-generation neutrino
has to be rather heavy (> M_Z/2), in sharp contrast to the other three
neutrinos, the underlying nature of the 4th-generation neutrino is expected to
be different. We suggest that an additional gauge symmetry B-4L_4 distinguishes
it from the Standard Model's three lighter neutrinos and this also facilitates
promotion of the 4th-generation predominantly right-handed neutrino to a good
cold dark matter candidate. It provides distinguishable predictions for the
dark matter direct detection and the Large Hadron Collider experiments.
