  We study parameters of an extended standard model. The neutrino sector is
enlarged by one or two right-handed singlet fields and the Higgs sector
contains one additional doublet. One-loop radiative corrections generate the
mass for the light neutrino fields. The numerical analysis is performed varying
the masses of heavy neutrinos and of the additional neutral Higgses. The
parameters of the neutrino sector, allowing for the seesaw type-I mechanism,
are restricted by experimental neutrino oscillation data. Both normal and
inverted hierarchies of the light neutrino masses are discussed.
