  An explicit mass formula is proposed for three active neutrinos and their
heavy sterile (righthanded) counterparts in the framework of seesaw mechanism.
The formula correlates reasonably the experimental estimates for the solar
$\Delta m^2_{12}$ and atmospheric $\Delta m^2_{32}$ in the case of hierarchical
spectrum $m^2_1 \ll m^2_2 \ll m^2_3 $ of active neutrinos. The lightest heavy
neutrino is predicted to be $O(10^5)$ times lighter than the heaviest. An
efficient mass formula, proposed previously for charged leptons, is recalled
and coordinated with the new mass formula for neutrinos.
