Grob et al.'s study is unique in the application of quantitative and rigorous methodology to study a religious group who have incorporated the plant hallucinogen ayahuasca into ritual practice over the last 35 years. While we know that such substances have a long and mostly unwritten history of use in the Amazon region of South America, such a study as the one presented for us in this Journal plays an important historic role. To my knowledge, it is the only experimental study in a natural context that enables us to make a measured judgment about outcomes and treatment efficacy. As American psychiatry considers embarking upon future ventures to integrate hallucinogenic substances into clinical practice, we are obliged to assess and evaluate their prior history of use.