  We study the special features emerging from a three lepton generation
analysis of the available neutrino oscillation data (solar, atmospheric and
LSND). First we find that it is possible to explain all three sets of data in
terms of the standard left handed neutrinos without the need of sterile
neutrinos. Second we find a significant difference in the mass matrix extracted
from the data, depending on the analysis (without or with LSND), if the mass of
the lightest neutrino, which cannot be determined from the neutrino oscillation
data alone, is relatively small, i.e $\leq$0.1 eV. To compare with other
processes we used the R-parity violating Minimal Supersymmetric Standard Model
(\rp-MSSM) for the theoretical description of the neutrino masses. Using the
oscillation data we were able to constrain the parameters of the model. In
particular we were able to obtain values for the coupling constants of the
\rp-MSSM.
