In the Stackelberg duopoly experiments in Huck et al. (2001), nearly half of the followers’ behaviours are inconsistent with conventional prediction. We use a test in which the conventional self-interested model is nested as a special case of an inequality aversion model. Maximum likelihood methods applied to the Huck et al. (2001) data set reject the self-interested model. We find that almost 40% of the players have disadvantageous inequality aversion that is statistically different from zero and economically significant, but advantageous inequality aversion is relatively unimportant. These estimates provide support for a more parsimonious model with no advantageous inequality aversion.