Neutrino mass and baryon-number nonconservation in superstring models

We propose new mechanisms for understanding neutrino masses in superstring models that contain ${\mathrm{E}}_6$-singlet zero-mass fields after compactification. We show that the low-energy gauge group of these models can be phenomenologically acceptable. We then comment on ΔB=1 and ΔB=2 baryon-number-violating processes in these models.