  After some general remarks about SU_L(4) electroweak unification, the model
is extended to SU_L(4)xU_X(1) to accomodate fractionally charged quarks. The
unification scale is expected to be in TeV region. A right-handed Majorana
neutrino along with known lepton are put in the fundamental representation of
SU_L(4) with Y_X=0. The see-saw mechanism for neutrino masses and flavor mixing
in neutrino sector is a natural feature of the model. The lepton number
violating processes can occure through dilepton gauge bosons contained in the
model.
