This paper examines a preference among rural Catholics in Northeast Brazil to treat generalized forms of malaise with isotonic solution administered intravenously, even where such treatment goes against biomedical advice. It situates this practice within a nexus of local ideas about the value of blood and sacrifice, which emerge out of socio-historical and environmental factors particular to the region. In this context blood is merely one in a sequence of substances linked to the regenerative martyrdom of Jesus, to the agricultural cycle, and to the economic struggle for existence in a drought-affected region. The materialization of blood, sweat, and tears on the surface of the body indexes social relationships built on sacrifice. The appearance of such substances, often between categories of close kin, are ideally characterized by the loss or flow of substance in a single direction. In such contexts replenishing the blood with isotonics maintains a uni-directional flow, preserving the value of sacrifice.