In the development of medical techniques and therapeutic agents, the transfer of knowledge produced in animal “models” to experimental settings involving humans is a crucial step. According to Canguilhem, an epistemological as well as a normative-ethical dimension may be distinguished in this context. This project looked into the practices and negotiations related to the transitions from experimenation with animals to human subjects. Using exemplary cases such as the “discovery” and “proof” of the antibacterial action of penicillin (in Britain) and sulfa drugs (in Germany) between the late 1920s and the early 1940s, the project analyzed the local settings with their specific material and technical resources and dynamics, the epistemological, political, and economic rationalities relevant for the transfer of knowledge between animal and human experimental systems, as well as the modifications that this knowledge itself underwent in the course of such transfer processes. Going beyond previous “national” narratives in the case of penicillin and sulfa drugs, a close reading of laboratory diaries, correspondence, and publications by the main historical actors revealed mutual perceptions, selective adaptations, and re-interpretations of practices and data of the respective “rivals” for specific local agendas, which in turn were heavily influenced by interests like commerce, and heated debates on the treatment of infected wounds during World War II. On another level, the project looked into the explicit and implicit assumptions of historical actors about the communalities and differences between animals and human beings, and their considerations about the conditions that had to be fulfilled to enable the step from animals to humans.