Here I present two cases of very recent introduction of the standard ayahuasca formula in two neighboring indigenous groups of the Manu River region in southern Peru: the Matsigenka and the Yora (Nahua). Although attesting to the historical dynamism of indigenous people and their shamanic practices, the case also raises questions about authenticity, tradition, and culture, and how these concepts are used as a litmus test to judge the bona fide status and legality of ayahuasca use in "nontraditional" urban settings around the world.