Abstract. In this paper, we contribute with empirical insight into the complexity of establishing and sustaining integration between different information infrastructures in health care. An overall concern is to elaborate on how, despite many obstacles, the integration effort moves forward. We see this as a collective achievement, where users have an essential role in terms of mobilizing and coordinating the other actors as well as maintaining the integration. These activities are not limited to a specific project; they emerge from and are part of day-to-day practice. Empirically, we focus on a large integration initiative between the laboratory systems at the University Hospital of Northern Norway and the electronic patient records used by general practitioners in the Northern health region. Together with the vendor, Well Diagnostics, the hospital initiated a project aimed at establishing a new laboratory requisition system that enabled GPs to send requisitions electronically to the hospital laboratories. Theoretically, we draw on the concept of information infrastructures, and supplement this with Actor Network Theory.