  We consider the two four-neutrino schemes that are compatible with all
neutrino oscillation data. We present the range of the corresponding mixing
parameters allowed by the results of neutrino oscillation experiments. We
discuss the implications for long-baseline experiments and we suggest the
possibility to reveal the presence of CP-violating phases through a comparison
of the oscillation probability measured in long-baseline experiments with the
corresponding average oscillation probability measured in short-baseline
experiments.
