  The hypothesis of an additional abelian symmetry acting in a different way on
the three families of leptons leads to interesting predictions in the neutrino
sector. Contrary to what happens in most seesaw models, the structures of the
Dirac and the Majorana matrices are determined without any ansatz, and the
neutrino masses and mixing angles are fixed once the lepton charges under the
family symmetry have been chosen. Two explicit models using this idea are
presented.
