  We show that a breakdown of the universality of the gravitational couplings
to different neutrino flavors can be tested in long-baseline
neutrino-oscillation experiments. In particular we have analyzed in detail a
proposed experiment at SOUDAN 2 with $\nu_\mu$ beams from the Fermilab Main
Injector. It turns out that we can study both masses of neutrinos and such a
breakdown with sensitivity to the order of $10^{-14}$ by investigating the
energy spectrum of the resulting muons.
