Human Embryonic Stem (hES) cell research has met with a mixed reception internationally, but in the UK remains a significant national priority. Management of what is called the ‘national embryo supply’ in the UK involves new forms of governance at the ‘IVF-Stem cell Interface’, where questions about the provenance of donated embryos, including the ethics of their sourcing, are at a premium. This article explores the question of embryo donation to stem cell research from the perspective of the increasing proximity of IVF and hES cell derivation, using a model of ‘double reproductive value’ to explore what forms of exchange and flow are occurring, and how these are defined and negotiated in the context of a national hES cell coordination network of practitioners.