This investigation tested whether social norms and endorsement of humanitarian values interact to influence authoritarians' attitudes toward immigrants. Oyamot, Borgida, and Fisher (2006) found correlational evidence for a model in which: (1) clear social norms for attitudes toward an outgroup (favorable or unfavorable) influence the authoritarianism–attitude relationship in the direction of the norm, and (2) in the absence of clear social norms, endorsement of humanitarian–egalitarian values attenuate the intolerant tendencies of authoritarians. The current investigation tested the model in a survey experiment conducted in a diverse adult sample (N = 388). We measured participants' levels of authoritarian predisposition and endorsement of humanitarian values. Participants were then randomly told that Americans in general had either negative, positive, or mixed opinions about immigrants and immigration (social norm condition), and then asked about their attitude toward immigrants. Consistent with the model, authoritarianism was negatively related to attitudes toward immigrants in the negative norm condition. However, authoritarians' tendency toward intolerance was attenuated when they thought that Americans in general had positive opinions about immigrants. Also as predicted, when societal norms were depicted as mixed, authoritarians' attitudes depended upon endorsement of humanitarian values: humanitarian authoritarians held positive attitudes and non-humanitarian authoritarians held the most negative attitudes toward immigrants. Implications for understanding the effects of authoritarian predispositions in varying social contexts are discussed.