  We study parity violation in $2+1$-dimensional gauge theories coupled to
massive fermions. Using the $\zeta$-function regularization approach we
evaluate the ground state fermion current in an arbitrary gauge field
background, showing that it gets two different contributions which violate
parity invariance and induce a Chern-Simons term in the gauge-field effective
action. One is related to the well-known {\em classical} parity breaking
produced by a fermion mass term in 3 dimensions; the other one, already present
for massless fermions, is related to peculiarities of gauge invariant
regularization in odd-dimensional spaces.
