Gender differences in mathematics test performance that favor males are rarely found on tests of computation or other mathematical symbol manipulations. They appear primarily in tests that are labeled as tests of mathematical reasoning and consist largely of word problems. The content of word problem cover stories is a possible source of gender bias. Some have suggested that students are discouraged from solving problems for affective reasons when the content of the problem is sex-typed for the opposite sex; cognitive science research on the problem solving processes suggests that familiarity of content would be likely to affect problem solving performance. To test these hypotheses, an experiment was conducted in which underlying mathematics problems were clothed in four different cover stories: masculine, feminine, neutral familiar and neutral unfamiliar. No effect of sex-typing was found; there was an highly significant but small effect of familiarity. Ratings of problem characteristics were also collected, primarily to guide and confirm the realization of the design intentions, and a number of interesting features of the rating results are discussed.