  We consider flavor changing effective neutrino interactions in the context of
massive neutrinos in the issue of atmospheric neutrinos. Assuming as usual that
this is an indication of the oscillation of muon neutrinos into tau neutrinos
we show that there is a set of parameters which is consistent with the MSW
resonance condition for the typical Earth density and atmospheric neutrino
energies. In particular we show that even if the vacuum mixing angle vanishes
it is still possible to have a resonance which is compatible with the
atmospheric neutrino data. We also briefly consider the case of the solar
neutrino problem.
