  By relating the Dirac neutrino mass matrix to the mass of the charged
fermions and assuming that the product of the masses of the two lightest
left-handed neutrinos is of the order of $\Delta m^2_{sol}$, we derive, within
a leptogenesis scenario, a range of values for the mass of the heaviest
right-handed neutrino, centered around the scale of $B-L$ symmetry breaking in
the SO(10) theory with Pati-Salam intermediate symmetry.
