  New measurements of the $\eta$ and $K^0$ masses have been performed using
decays to 3$\pi^0$ with the NA48 detector at the CERN SPS. Using symmetric
decays to reduce systematic effects, the results $M(\eta) = 547.843\pm0.051$
MeV/c$^2$ and $M(K^0) = 497.625\pm0.031$ MeV/c$^2$ were obtained.
