The morphological changes occurring during the phase inversion of a polystyrene/polyethylene blend subjected to isothermal, steady shear flow are investigated and characterized. The isothermal, steady shear flow field provides a well-defined thermal and flow history. This contrasts with previous work on phase inversion, which was conducted in complex flow fields with large temperature gradients. The well-defined flow field permits a more detailed examination of the sequence of morphological changes during phase inversion than was accomplished previously. Both components are observed to initially deform into a sheet morphology. At strains of 200-780, the (initially continuous) minor component begins to break up, allowing the (initially dispersed) major component to coalesce. The blend becomes co-continuous around strains of 330-1500. At strains of 500-2000, the major component continues coalescing. The minor component breaks up into fibers and drops at strains of 800-3000. Breakup of the minor-component sheets is not observed until the sheets are less than 1 mu m thick. Deformation and breakup of the initially dispersed phase is observed in this shear flow field, despite a viscosity ratio in excess of 10. For the system studied here, phase inversion does not occur under no-flow conditions.