Through a comparative analysis of Human Rights groups in Kenya and Cameroon, our study demonstrates that Human Rights, as a discourse of protest, are not universally efficient. Whatever the universal acceptance of Human Rights, non-governmental organisations that defend them are heavily dependent on the conditions of collective action prevalent in contexts of recent political liberalisation. The creation and institutionnalization of Human Rights NGOs illustrate the tensions between the historical constraints and the margins of innovation underlying any collective action. If the new or mimetic structures of the NGOs reflect the possibilities of invention in a constraining political environment, the emergence of Human Rights activists is often framed by the history of political opposition in each country. Also, while the relative flexibility of their repertoires of action allow for the diffusion of Human Rights through a variety of media, historically-constructed discourses and symbols are a crucial factor in the enunciation and legitimation of Human Rights. Finally, if the interactions of NGOs with the State change progressively, they are primarily framed by history, and the influence of Human Rights NGOs over public policies is restricted by the internal limits of the Human Rights discourse itself and those of the reforms conducted on their behalf. This research thus argues that Human Rights are relevant research objects in the exploration of the political cultures and institutional mechanisms of regimes ; it shows however that they are neither a sufficient nor an efficient way of bringing about political change.