Precise Measurement of the ? and K0 Masses

New measurements of the ? and K0 masses have been performed using decays into 3?0 with the NA48 detector at the CERN SPS. Using symmetric decays to reduce systematic effects, the results M(?) = 547.843 ? 0.051 MeV/c2 and M(K0) = 497.625 ? 0.031 MeV/c2 were obtained.