This paper reported three studies examining the role of working memory capacity in stereotype threat. Working memory capacity refers to a memory system responsible for focusing attention on task-relevant information while inhibiting task-irrelevant thoughts. Effective utilization of working memory capacity is central for successful performance on cognitive tasks, and failures in working memory have been suggested as responsible for performance decrements under stereotype threat. These studies provided the most direct test to date of the possibility that stereotype threat might diminish working memory capacity. In these studies, participants were asked to solve math problems while also keeping a set of words in memory. Later recollection of the set of words was used as an index of working memory capacity. If few words could be recalled, for example, that would suggest that the math problems required more working memory. Results confirmed that stereotype threat reduces working memory capacity that is at least partially responsible for performance decrements under stereotype threat. In Experiment 1, participants were presented with a task described as either requiring "quantitative capacity" that might account for gender differences in math performance (stereotype threat for females), or as a task involving working memory capacity (control). Only women in the stereotype threat condition recalled significantly fewer words, indicating reduced working memory capacity. Experiment 2 showed similar effects comparing Latino and White students, where stereotype threat was created by describing the task as reflecting general intelligence; only Latinos under stereotype threat showed lower word recall. Experiment 3 manipulated stereotype threat by having women solve math problems in a group of other female students (control), or as the sole woman in a group of men (stereotype threat). Working memory capacity and performance on a math task were both lower in the latter group, and the reduction on working memory capacity statistically mediated the relation between stereotype threat and math performance. These studies suggest that stereotype threat can disrupt the ability to maintain proper focus on task-relevant information.