We study the magnetic field dependence of muonium--antimuonium conversion induced by neutral (pseudo)scalar bosons. Only the SS operator contributes to the conversion of polarized muonium, but it gets quenched by a magnetic field of strength 0.1 Gauss or stronger. Conversion induced by SS couplings for unpolarized muonium is independent of magnetic field. Magnetic fields of 0.1 Tesla or stronger starts to suppress conversion induced by PP interactions in the lowest Breit-Rabi level, but gets

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... tially compensated by a rise in conversion probability in the other unpolarized level. The effects of (S∓ P)(S∓ P) and (S∓ P)(S± P) operators behave in the same way as (V∓ A)(V∓ A) and (V∓ A)(V± A) operators, respectively.