This study examines physics students' evaluations of identical, video-recorded lectures performed by female and male actors playing the role of professors. The results indicate that evaluations by male students show statistically significant overall biases with male professors rated more positively than female professors. Female students tended to be egalitarian, except in two areas. Female students evaluated female professors' interpersonal/communicative skills more positively than male professors'. They evaluated female professors' scientific knowledge and skills less positively than that of male professors just as male students did. These findings are relevant to two areas of research on bias in evaluation: rater-ratee similarity bias and stereotype confirmation bias. Results from this study have important implications for efforts