Research participants' sexual orientation is not consistently taken into account in experimental psychological research. We argue that it should be in any research related to participant or target gender. Corroborating this argument, an example study is presented on the gender bias in face recognition, the finding that women correctly recognize more female than male faces. In contrast, findings with male participants have been inconclusive. An online experiment (N = 1,147) was carried out, on purpose over-sampling lesbian and gay participants. Findings demonstrate that the pro-female gender bias in face recognition is modified by male participants' sexual orientation. Heterosexual women and lesbians as well as heterosexual men showed a pro-female gender bias in face recognition, whereas gay men showed a pro-male gender bias, consistent with the explanation that differences in face expertise develop congruent with interests. These results contribute to the growing evidence that participant sexual orientation can be used to distinguish between alternative theoretical explanations of given gender-correlated patterns of findings.