  If cosmic strings are present at the electroweak phase transition, they can
act as seeds on which bubbles of true vacuum nucleate. We explore the nature of
such a phase transition, in particular the wall velocity and thickness of the
bubbles. {}From the viewpoint of electroweak baryogenesis, adiabatic conditions
exist in the expanding bubble walls, and such models of baryogenesis can be
successfully applied. In the present mechanism, the nature of the electroweak
phase transition is insensitive to the other details of the model, thus
reducing the uncertainties in the estimate of net baryon asymmetry.
