Abstract
The see-saw mechanism is a very attractive explanation for
small neutrino masses, parametrized at the GUT scale by the
right-handed Majorana mass matrix, 
, and the neutrino Yukawa
matrix, Yν. We show that in a SUSY model with universal
soft terms, and Yν can be calculated from the
light neutrino masses, the MNS matrix, and Y†νYν, which enters into the left-handed slepton radiative
corrections. This suggests that in principle the GUT-scale
inputs of the seesaw could be reconstructed from the neutrino and
sneutrino mass matrices. We briefly discuss why this is impractical,
but advocate the neutrino and sneutrino mass matrices as an
alternative bottom-up parametrization of the seesaw.