Adele Clarke’s Disciplining Reproduction (1998) argued that the reproductive sciences gained legitimacy between the early 1920s and the late 1940s through the circulation of biological materials, tools, techniques, people and concepts between the three social worlds of biology, medicine and agriculture, and suggested that the physiological speciality of endocrinology became a shared reference point. This chapter revisits Clarke’s argument by focusing on the trajectories, multiple uses and diverse roles played by sex hormones in the twentieth-century history of the reproductive sciences. It thus enlarges the horizon in three ways. First, it brings in the European scene. Second, benefiting from new historical writing on drugs and therapeutic agents, it argues for the critical impact of industrial pharmacy, a social world missing from Clarke’s scheme. Third, it shows how taking into account the centrality of biochemically defined sex hormones helps us understand the most recent transformation of the reproductive sciences, their increasing marketization, encompassing of risk prevention and incorporation of activism—in a word, their ‘biomedicalization’. It thus distinguishes three eras: of professionals and physiology, of industrialists and biochemists, and of consumers, public regulation and experts in risk.