Sex hormones today are seen as central to the production of biological sexual difference. This article examines the development of this scientific `fact', and asks how hormones came to be in this position. The article does not involve original historical research, however. Instead it uses existing histories of hormonal sexual difference to develop a theoretical argument about body histories. How can the history of scientific views of bodies be written and understood? What can these histories tell us about the relation between scientific representations of bodies and the materiality of bodies? Combining and critiquing arguments from feminist histories of science, Bruno Latour's actor network theory, Michel Serres's theory of folded time, and Donna Haraway's notion of situated knowledges, this article argues for the centrality of embodiment and location to useful body histories.