Based on previous research investigating proscriptive injunctions (requesting that one should not do something) versus prescriptive injunctions (requesting that one should do something), we propose that proscription leads to greater reactance than does prescription for a range of actions, and that this effect is associated with lower perceived legitimacy of the injunction. Across five experimental studies, our student and general population samples received proscriptions or prescriptions and reported their reactance. Proscription led to greater reactance than did prescription in all five studies. This effect was accentuated by an authoritative source (Study 2), was mediated by the perceived legitimacy of the request (Study 3 and Study 4), and was attenuated by a self-affirmation intervention (Study 5). We suggest that proscriptions are viewed as more obligatory than prescriptions, limit the scope of behavioral alternatives, restrict perceived autonomy, and elicit greater reactance. The findings have implications for the design of effective persuasive communications.