  There are several indications that the Majorana masses of the right-handed
neutrino components, $M_R,$ are at the intermediate scale: $M_R\sim
(10^{10}-10^{12})$ GeV or even lighter. The renormalization effects due to
large Yukawa couplings of neutrinos from region of momenta $M_R \ltap q \ltap
M_G$ are studied in the supersymmetric standard model. It is shown that
neutrino renormalization effect can increase the $m_b/m_\tau$ ratio up to
$(10\div 15)\%.$ This strongly disfavours $m_b-m_\tau$ unification for low
values of $\tan\beta < 10$ especially at large values of $\alpha_s.$ Lower
bounds on $M_R$ and $\tan\beta$ from the $b-\tau$ unification condition were
found. The implications of the results to the see-saw mechanism of the neutrino
mass generation are discussed.
