The biographical-narrative approach has been gaining ground in the areas of science studies and social sciences (Shortland and Yeo 1996; Huisman et al. 2000; Plummer 2001) . We find examples of this approach in anthropological laboratory studies (Traweek 1988) , feminist studies of science (Abir-Am and Outram 1987), the sociology of science (Zuckerman 1977; Goodell 1977; Kissmann 2007) , the history of science (Porter 2006; Nye 2006; Terrall 2006) and the epistemology of science (Zwart 2008). The biographical-narrative method used here combines socialhistorical studies and narrative analysis, and provides an idiographic view on expertise in the form of 'expert narratives'. To produce these narratives, data from various types and sources were ordered around a specific 'plot' or thematic thread Virology Experts in the Boundary Zone 147 (Polkinghorne 2005, p. 69) : the advancement of virologists from laboratory experts into experts on policy and the public domain. The inductive development of narratives involved four iterative stages. In the first stage, data were collected on the academic and public track records of the three virologists, and on the socio-historical context of infectious diseases in which these virologists were situated. This was used to prepare biographical-narrative interviews, 1 the second step. These interviews focused on their experiences in policymaking and public debate. The experts also commented on each other in these interviews. The third step was to organise the data temporally, hereby focusing on the diachronic data (data on events, their relations and the effects of events). This step included the collection of additional data, for example by conducting a second round of interviews. In the final stage, the expert careers were written down as coherent and empirically-grounded narratives, thereby 'explicating an intrinsically meaningful form' (Polkinghorne 2005, p. 93) .