  An extension of the gauge group $SU(2)_L\otimes U(1)_Y$ of the standard model
to the symmetry group $SU(4)_L\otimes U(1)_X$ (3-4-1 for short) is presented.
The model does not contain exotic electric charges and anomaly cancellation is
achieved with a family of quarks transforming differently from the other two,
thus leading to FCNC. By introducing a discrete $Z_2$ symmetry we obtain a
consistent fermion mass spectrum, and avoid unitarity violation of the CKM
mixing matrix arising from the mixing of ordinary and exotic quarks. The
neutral currents coupled to all neutral vector bosons are studied, and by using
CERN LEP and SLAC Linear Collider data at Z-pole and atomic parity violation
data, we bound parameters of the model related to tree-level $Z-Z^\prime$
mixing. These parameters are further constrained by using experimental input
from neutral meson mixing in the analysis of sources of FCNC present in the
model. Constraints coming from the contribution of exotic particles to the
one-loop oblique electroweak parameters $S$, $T$ and $U$ are also briefly
discussed. Finally, a comparison is done of the predictions of different
classes of 3-4-1 models without exotic electric charges.
