Neutrino mixing and masses from long baseline and atmospheric oscillation experiments

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.