In 1986, Loren Miller, then director of a small U.S. pharmaceutical company, obtained a patent on a variety of ayahuasca, a hallucinogenic plant used by Amazonian indigenous people during religious rituals. Denounced as an act of biopiracy, the patent was legally challenged in 1999 by three non governmental organisations. This study aims at deepening our understanding of the ways in which patents on living organisms are challenged by focusing on the ayahuasca patent case, in particular through an argumentative analysis of the challenge. That case occupies a singular position amongst challenged patents, notably because it emphasises a relatively neglected issue in the debates around biopiracy : the respect of cultural specificities. Therefore, the ayahuasca case opens up the reflexion about the argumentative content of those debates and the power relations characterising them. Indeed, it raises the question of a more substantial integration of the respect of cultural specificities in the debates around biopiracy, which usually center on issues such as equity, environmental conservation or food safety.