The Bystander Intervention Model (BIM) is applied to explore how bystanders to workplace bullying assess situations and choose responses based on the (female) target's sexual orientation. We investigate how attitudes of homophobia and amnestic heterosexism (AH) affect these responses. Vignettes of workplace mistreatment against lesbian, female bisexuals, or female heterosexual targets were randomly presented to respondents, who were asked to assess the degree of "mistreatment" they perceive, their feelings of personal responsibility, and their anticipated responses. Analysis of covariance was used to analyze the data. Regardless of levels of homophobia or AH, respondents report less active intervention when the target is lesbian compared to bisexual or heterosexual females. Respondents do not distinguish between conditions in clarity or severity of bullying. However, those higher in homophobia and AH feel less personal responsibility and are less likely to intervene when the target is lesbian.