Contemporary use of ayahuasca in Amazonian mestizo populations appears to be an amalgam of diverse tribal traditions. The large urban settlements have become melting pots; people of many different cultural backgrounds have migrated to these centers in search of employment in the timber, petroleum, and similar resource-based industries, and have brought with them their own tribal traditions and belief systems (usually syncretically fused with Christianity due to prior contact with missionaries). The cultural background of these migrant laborers often extends to a knowledge of the medicinal plants valued in their own culture; over the years this drug-plant lore derived from diverse sources has gradually diffused through the larger mestizo society and become melded into various systems of traditional medicine. This tradition, though it incorporates elements of its diverse tribal origins, is at the same time unique to the mestizo social class. This process of cultural amalgamation has occured over the same period of time that most of the tribal societies in which reside the antecedents of mestizo folk medicine have disintegrated and/or disappeared. As a result mestizo folk-medicine as it is practiced today in the urban centers of the Amazon is a living system of traditional medicine based on the ethnomedicine of many cultures; in many cases it is the only place where such knowledge has been preserved. Hence it is important, even urgent, that mestizo folk-medicine and the plants that form its basis be studied by investigators with scientific backgrounds in medicine, pharmacology, phytochemistry, and botany while the opportunity still exists. This paper presents ethnobotanical and phytochemical information on approximately 50 genera of medicinal plants which are utilized as ayahuasca admixtures in contemporary mestizo folk medicine.