  A new result from searching for muonium to antimuonium conversion is reported
which sets an upper limit on the coupling constant in an assumed $(V-A) \times
(V-A)$ type interaction of $G_{M\bar{M}} \leq 3\cdot 10^{-3} G_F$ ~ (90% C.L.).
  A particular Z_8 and a minimal 331 GUT model can be ruled out. Further new
and stringent limits can be set for masses of bileptonic gauge bosons and
$\lambda$ parameters in R-parity breaking supersymmetric models.
