This article develops an anthropology of the body in its material and social environment among the Cashinahua (Huni Kuin) from Brazilian and Peruvian Amazonia. The Cashinahua body, it shows, is thought of as produced by others, not as growing naturally. Growth can be defined as the corporeal accumulation of knowledge in the form of "soul." The article describes the verbal, medical, and other techniques used to transform it into "a body that knows." In the Cashinahua understanding, a healthy body is one that constantly learns through the senses and expresses the accumulated knowledge in social action and speech. An ill body is one that no longer knows. Curing, therefore, acts to restore a person's capacity to know. The whole article defends the proposition, then, that a prior condition for any medical anthropology in the Cashinahua case is a thorough examination of Cashinahua epistemology. Finally, through comparative discussion of other peoples in lowland South America, it seeks to show that this is also the case more widely in the ethnographic region. Ultimately, it suggests that ethnography in lowland South America undermines the possibility of a "medical anthropology" per se.