This study compared the biomechanical support offered by eight presently marketed sports bras for small-, medium-, and large-breasted women while jogging. Fifty-nine subjects were filmed while jogging on a treadmill in each of the bras and in the nude condition. The vertical displacement of the breast relative to the body during one average running stride was calculated for each condition. An ANOVA and pairwise difference procedures revealed significant differences between the D cup size group and each of the remaining three cup size groups in the nude condition. In addition a two-way repeated measure ANCOVA indicated significant pairwise differences among the bras; both within each cup size group, and within the group as a whole. Implications for future biomechanical breast research and sports bra design are discussed. (Author/JD)