The use of the psychedelic vine, ayahuasca (various Banisteriopsis species), in the Peruvian Amazon by mestizo folk healers is related to such variables as cultural expectations of drug experience and belief systems concerning illness. A subjective personal experience inherent in psychedelic use takes on cultural coloration, as determinants of hallucinatory experience show strong relationships to cultural data. [ayahuasca, hallucinogens, folk medicine, medical anthropology, psychedelics]