  The geometric phase for neutrinos propagating in an adiabatically varying
magnetic field in matter is calculated. It is shown that for neutrino
propagation in sufficiently large magnetic field the neutrino eigenstates
develop a significant geometric phase. The geometric phase varies from 2$\pi$
for magnetic fields $\sim$ fraction of a micro gauss to $\pi$ for fields $\sim
10^7$ gauss or more. The variation of geometric phase with magnetic field
parameters is shown and its phenomenological implications are discussed.
