Information on 50 medicinal plants used by the Ese'eja, a group of amerindians belonging to the takana linguistic family that lives in Madre de Dios, Peru, was collected during an ethnobotanical expedition to south-western Amazonia. A description of shamanic practices is given to understand better the position of health practices in this culture, which includes the use of medicinal and ritual plants. Fragments of 'ayahuasca' ritual in shamanic initiation and in healing rituals are presented. Different extracts of plants were studied for bioactivity according to their use and accessibility. The bioassays used were: the brine shrimp cytotoxicity assay, the wheat rootlet growth inhibition assay and the DNA-methyl green assay. The results obtained and their possible corelation with the ethnomedical use are discussed.