Past research suggests that reactions to research on sex differences are often less positive when the findings put men in a better light than women, especially when the lead researcher is a man. The factors underlying this effect, however, are not yet fully understood. The present study aimed to provide the first experimental test of the hypothesis that the key variable is perceived harm to women. Participants (214 men and 219 women) evaluated a bogus popular-science article reporting fictional research finding either a female- or a male-favouring sex difference in intelligence, attributed to either a female or a male lead researcher. To examine the effects of perceived harm, the introduction to the task highlighted either the potential benefits or potential drawbacks of sex-differences research in general. Consistent with past research, participants reacted less positively to the male-favouring difference, especially for male-led research. Consistent with the harm hypothesis, the effect was stronger after highlighting the potential drawbacks of sex-differences research than after highlighting the potential benefits. Our findings suggest that perceptions of harm to women underpin the aversion to male-favouring findings.