Thinking with the vital materiality of placentas as it is evinced in a placental stem cell research lab in Korea, this article explores the relations and practices of care that are essential to the circulation of biological matters as infrastructure of tissue economies. I attend to the flows of care that sustain tissue economies with the notion of ‘placental economies’. Shifting attention from donor subjects and tissue objects to practices and relations of care as an infrastructure for the circulation of tissues, I explore how the vitality of biological matters is an achievement made and sustained through the relations and practices of care that animate the placenta in different forms. On the basis of an ethnographic fieldwork conducted in Korea, this article focuses on two different forms of care (lab workers’ care of cells, and pregnant women’s care of fetuses) that enable the (re)production and circulation of placenta-derived stem cells possible. I argue that the flows of tissues and vitality are indeed the flows of care, as an anticipatory as well as responsive practices, without which the vitality cannot exist in its current form. Furthermore, I suggest that relations and practices of care are a kind of infrastructure of promissory biotechnological enterprises.