Of the numerous plant hallucinogens utilized by indigenous populations of the Amazon Basin, perhaps none is as interesting or complex, botanically, chemically, or ethnographically, as the hallucinogenic beverage known variously as ayahuasca, caapi, or yage. The beverage is most widely known as ayahuasca , a Quechua term meaning "vine of the souls," which is applied both to the beverage itself and to one of the source-plants used in its preparation, the Malpighiaceous jungle liana, Banisteriopsis caapi (Schultes, 1957). In Brazil, transliteration of this Quechua word into Portuguese results in the name, Hoasca. Ayahuasca, or hoasca, occupies a central position in Mestizo ethnomedicine, and the chemical nature of its active constituents and the manner of its use makes its study relevant to contemporary issues in neuropharmacology, neurophysiology, and psychiatry.