  We study the physical reach of a Neutrino Factory in the 2+2 and 3+1 Four
Neutrino mixing scenarios, with similar results for the sensitivity to the
mixing angles. Huge CP-violating effects can be observed in both schemes with a
near, O(10) Km, detector of O(10) Kton size in the $\nu_\mu \to \nu_\tau$
channel. A smaller detector of 1 Kton size can still observe very large effects
in this channel.
