  We construct field configurations that interpolate between string background
states of differing baryon number. Using these configurations we estimate the
effect of the background fields on the energy barrier separating different
vacua. In the background of a superconducting GUT string the energy barrier is
increased, while in an electroweak string background or the electroweak layer
of a non-superconducting string the energy barrier is reduced. The energy
barrier depends sensitively on both the background gauge and scalar fields.
