  It is shown that the equation for Green's function of fermions (neutrinos)
with weak interactions (in matter) coincides with the equation for Green's
function of fermions in vacuum. This result is a consequence of the fact that
the right components of fermions do not participate in weak interactions. As a
result we come to a conclusion: the mechanism of resonance enhancement of
neutrino oscillations in matter (i.e. MSW effect) cannot exist.
