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 $G_{Mbar{M}} leq 3cdot 10^{-3} G_F$ ~ (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.
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