This paper follows the trajectory of sex steroids in 1930s Germany as a way to investigate the system of research which characterized the development of these drugs. Analyzing the changing relationship between the pharmaceutical company Schering and the Kaiser Wilhelm Institute für Biochemie headed by Nobel Prize winner Adolf Butenandt, the paper highlights the circulation of materials, information and money as much as the role of patents in shaping the study of sex steroids. Semi-synthetic analogs and metabolic pathways thus emerged (...) as shared bio-industrial assets. This collaborative work participated in a more general ‘internalization’ of biology, which took place in pharmaceutical firms during the 1920s and 1930s as a strategy to standardize and develop biologicals. The construction of the hormone market was also based on Schering’s collaboration with a selected group of clinicians who worked out the wide-range of indications associated with these ‘natural’ drugs. The paper finally shows how the wartime scientific and industrial mobilization in Nazi Germany marginalized the study of sex steroids and led to the dismantling of the KWIB–Schering network. (shrink)