The present research examined the hypothesis that heterosexual men’s motivation to differentiate their ingroup from gay men moderates the link between egalitarianism and sexual prejudice. In two experiments conducted in Switzerland ( N = 74) and Ecuador ( N = 104), we assessed heterosexual men’s endorsement of egalitarian values and experimentally manipulated scientific evidence supporting or refuting the existence of biological differences between heterosexual and gay men (the biological theory). The main dependent variable was attitude towards homosexuality. As predicted, the interaction between egalitarianism and the biological theory was significant in both experiments, t (67) = 3.18, p = .002, η _p ² = .13, and t (100) = 2.26, p = .026, η _p ² = .04, respectively. Egalitarianism increased positive attitudes towards homosexuality only when science supported the existence of biological differences between heterosexual and gay men. We discuss the relevance of this finding to intergroup relations.