The effect of prestraining at a fast strain rate (region III) on the subsequent superplastic behaviour (region II) of a 7475 Al alloy has been studied. The results show that prestraining causes a decrease in the elongation to failure as compared to the non-prestrained (as-received) samples. This decrease in elongation is postulated to be associated with the growth of cavities formed during prestraining as well as grain growth during deformation in region II. Prestraining in region III did not lead to any observable inhomogeneities in strain distribution during subsequent deformation.