Recent theory and research suggests that labile self-esteem (SE) is an important dimension of vulnerability to depression (Butler, Hokanson, & Flynn, 1994; Roberts & Monroe, 1992, 1994, in press). In the present study, participants completed seven daily ratings of SE from which we derived a measure of lability. The interaction between labile SE and life stress predicted increases in depressive symptoms across a two-month prospective interval, particularly in participants who were initially low in depression and who had more severe worst lifetime episodes of depressive symptomatology. Interactions between life stress and labile SE were stronger for life stress measures that were based on the subjective appraisal of stress than for those that were based on raw life event counts. In contrast to predictions, depletions in self-esteem failed to mediate the synergistic effects of labile SE and life stress.