  The atmospheric and solar neutrino oscillation data suggest hierarchical
neutrino masses with at least one large mixing. The simplest see-saw models for
reconciling the two features are U(1) extensions of the SM with flavour
dependent gauge charges. I discuss a minimal model of this type containing two
heavy right-handed neutrinos, which have normal Dirac couplings to $\nu_\mu$
and $\nu_\tau$ but suppressed ones to $\nu_e$. It can naturally account for the
large (small) mixing solutions to the atmospheric (solar) neutrino oscillation
data.
