Heavy neutrino mass scale and quark-lepton symmetry

Assuming hierarchical neutrino masses we calculate the heavy neutrino mass scale in the seesaw mechanism from experimental data on oscillations of sol ar and atmospheric neutrinos and quark-lepton symmetry. The resulting scale is around or above the unification scale, unless the two lightest neutrino s have masses of opposite sign, in which case the resulting scale can be in termediate. (C) 2000 Elsevier Science B.V. All rights reserved.