Electric and magnetic charges in superstring models

We investigate the allowed values of magnetic and electric charge in superstring models in which a grand unified O(10) or E6 gauge group is broken by Wilson lines. In general, the minimum value of magnetic charge is not the Dirac quantum 2π/e but an integer multiple of it. Conversely, the quantum of electric charge (for unconfined, color singlet particles) is less than the charge of the electron by the same ratio.