  We discuss the relation between the CP symmetry and the custodial $SU(2)$
symmetry in the Higgs sector. In particular, we show that CP violation in the
Higgs-gauge sector is allowed only if the custodial $SU(2)$ symmetry is broken.
We exploit these facts to constrain CP violation using the experimental bounds
on $\rho-1$. CP nonconservation in the Higgs-fermion interactions can also be
constrained in a similar way although a possible exception is pointed out.
