  We derive renormalization group equations for neutrino masses, leptonic
mixing angles and CP-violating phases running at energies above the seesaw
threshold, both in the Standard Model and in the Minimal Supersymmetric
Standard Model extended with three right-handed neutrinos. With these
equations, we carry out a systematic study of the radiative correction that may
arise to neutrino parameters, via their renormalization group evolution from
the electroweak scale ($M_{\rm Z}$) to the scale of Grand Unified theories
($\Lambda_{\rm GUT}$). We study in detail three typically interesting neutrino
mass patterns: normal hierarchy, near degeneracy and inverted hierarchy.
Magnitudes of possible corrections in each case are carefully investigated. We
also emphasize the significance of CP-violating phases in controlling the
evolution behavior of all neutrino parameters.
