  We study the possibility of realizing the neutrino seesaw mechanism in the
E8XE8 heterotic string. In particular, we consider its Z_6 orbifold
compactifications leading to the supersymmetric standard model gauge group and
matter content. We find that these models possess all the necessary ingredients
for the seesaw mechanism, including the required Dirac Yukawa couplings and
large Majorana mass terms. We argue that this situation is quite common in
heterotic orbifolds. In contrast to the conventional seesaw of grand unified
theories (GUTs), no large GUT representations are needed to generate the
Majorana mass terms. The total number of right--handed neutrinos can be very
large, up to O(100).
