  Recent work on analytical solutions to the MSW equations for three neutrino
flavours is reviewed, with emphasis on the exponential density. Application to
a particular mass matrix, proposed by Lehmann, Newton and Wu, is also
discussed. Within this model, the experimental data allow a determination of
the three neutrino masses. They are found to be 0.002-0.004, 0.01 and 0.05 eV.
