  We show that even moderate excess of neutrons over protons in nuclear matter,
such as in ${}^{208} Pb$, can lead to large $\rho$-$\omega$ mixing at densities
of the order of twice the nuclear saturation density and higher. The typical
mixing angle is of the order of $10^o$. The mixing may result in noticeable
shifts of the positions and widths of resonances. We also analyze temperature
effects and find that temperatures up to 50 MeV have practically no effect on
the mixing.
