This study examines tools and practices involved in a large scale and multi-sited clinical trial of a potential drug against obesity. Two tools are in focus: a clinical research protocol and a computer control system. The analysis is based on there being different ways in which the tools are localized in order for the work to flow smoothly and to produce reliable data. It does this through delineating different types of work performed: production tasks, classical managerial work, compliance work and the work of coordinating beliefs and goals. The study is based on interviews, observations and documentary analysis. Through describing these types of work and how it is organized, the study emphasizes the trial as being part of an industrial production process. Hence, the tools are used not only to produce reliable data, but also to manage the work of the tools’ users in order to enable a smooth production process. In line with such a description, the protocol and computer control system are seen as objects that discipline practice, something that also resonates in the way staff talk about their work. The dissertation shows how the tools, despite this, leave room for aspects of clinical trial work that are both rational/technical and experiential/contingent. The dissertation also shows that obesity is enacted in different ways in the practices performed in the trial. Making sense of these somewhat contradictory enactments requires work referred to as coordination of beliefs about what obesity is, as well as of the different goals of the trial. By such a focus on invisible work, the dissertation shows that those nurses, dieticians and doctors involved in the everyday follow-through of the trial have a strategic position in mediating between pharmaceutical companies and their potential market for the drug under study, namely the trial participants.