Generally, superplastic deformation is accompanied by concurrent grain growth. In this paper, the effect of strain reversals on this process is investigated using two materials. In the first, Coronze 638, a precipitate strengthened copper alloy, no effect is found. In the second, Zn–22Al (wt-%) eutectoid, a distinct retardation of grain growth occurs after each strain reversal. A new model based on the ability of grain boundary sliding to overcome the Zener drag process is developed and found to be consistent with the experimental results.MST/731