This paper examines heterosexual adults attitudes toward bisexual men and women using data from a 1999 national RDD survey (N = 1,335). Ratings on 101-point feeling thermometers were lower (less favorable) for bisexual men and bisexual women than for all other groups assessed--including religious, racial, ethnic, and political groups--except injecting drug users. More negative attitudes toward bisexuals were associated with higher age, less education, lower annual income, residence in the South and rural areas, higher religiosity, political conservatism, traditional values concerning gender and sexual behavior, authoritarianism, and lack of contact with gay men or lesbians. White heterosexual women expressed significantly more favorable attitudes than other women and all men. A gender difference was observed in attitudes toward bisexuals and homosexuals: Heterosexual women rated bisexuals significantly less favorably than they rated homosexuals, regardless of gender, whereas heterosexual men rated male targets less favorably than female targets, regardless of whether the target was bisexual or homosexual.