  In this work we analyze the effects of quantum decoherence upon the
precession of the neutrino polarization vector in a supernovae-like
environment. In order to perform the study we have determined the
time-dependence of the polarization vector by solving the equation of motion
for different neutrino-mixing schemes. The results of the calculations show
that the onset of decoherence depends strongly on the parameters of the adopted
mixing scheme. As examples we have considered : a) the mixing between active
neutrinos and b) the mixing between active end sterile neutrinos.
