Blood samples collected from members of indigenous communities in the mid-20th century by scientists interested in human variation remain frozen today in institutional repositories around the world. This article focuses on two such collections—one established and maintained in the United States and the other in Australia. Through historical and ethnographic analysis, we show how scientific knowledge about the human species and ethical knowledge about human experimentation are coproduced differently in each national context over time. Through a series of vignettes, we trace the attempts of scientists and indigenous people to assemble and reassemble blood samples, ethical regimes, human biological knowledge, and personhood. In including ourselves—a U.S. historian of science and an Australian anthropologist—in the narrative, we show how humanistic and social scientific analysis contributes to ongoing efforts to maintain indigenous samples.