  We argue that regardless of the outcome of future Long Baseline experiments,
additional information will be needed to unambiguously decide among the
different scenarios of neutrino mixing. We use, for this purpose, a simple test
of underground data: an asymmetry between downward and upward going events.
Such an asymmetry, in which matter effects can be crucial, tests electron and
muon neutrino data separately and can be compared with the theoretical
prediction without relying on any simulation program.
