  Starting with the relation between two kinds of neutrino field operators
corresponding to definite flavor and mass states, we investigate if the usual
evolution relations for neutrino oscillation in matter can be consistently
derived, in the case of high energy neutrinos. A negative answer is obtained
contrary to an earlier result [P. D. Mannheim, Phys. Rev. D {\bf 37} (1988)
1935]. The reason for such a difference relies essentially on the Bogolyubov
transformation between two kinds of momentum-helicity creation- and
annihilation-operators with definite flavors and masses, which was not taken
into account in previous treatments.
