  We show that in 3-3-1 models it is possible to implement an extremely flat
scalar potential, i.e., a zero contribution to the cosmological constant, and
still having realistic values for the masses of the scalar Higgs fields.
Besides, when loop corrections are considered they impose constraints over
heavy particles masses (exotic quarks and extra vector bosons) which are
present in the model. A crucial ingredient in 3-3-1 models is the existence of
trilinear terms in the scalar potential. We also consider the two-Higgs
doublets extension of the standard model with and without supersymmetry.
