  In this talk, we discuss the implications of the renormalization group
equations for the neutrino masses and mixing angles in a supersymmetric
string-inspired SU(4) x SU(2)_L x SU(2)_R x U(1)_X model with matter in
fundamental and antisymmetric tensor representations only. The quark, charged
lepton and neutrino Yukawa matrices are distinguished by different
Clebsch-Gordan coefficients due to contracting over SU(4) and SU(2)_R indices.
In order to permit for a more realistic, hierarchical light neutrino mass
spectrum with bi-large mixing a second U(1)_X breaking singlet with fractional
charge is introduced. By numerical investigation we find a region in the model
parameter space where the neutrino mass-squared differences and mixing angles
at low energy are consistent with experimental data.
