  The decay KS -> 3pi0 is forbidden by CP conservation. Using a sample of more
than 6 million K -> 3pi0 decays, the NA48 Collaboration has improved the limit
on eta_{000} = A(KS -> 3pi0)/A(KS -> 3pi0) and on the branching ratio Br(KS ->
3pi0) by about one order of magnitude. Using this result and the
Bell-Steinberger relation, a new limit on the equality of the K0 and K0bar
masses is obtained improving by about 40% the test of CPT conservation in the
mixing of neutral kaons.
