This paper examines the recent public controversy sparked by the laboratory creation of a strain of highly pathogenic avian influenza transmissible among mammals. The contours of the controversy can be understood by tracking the assemblage of actors, institutions and devices gathered together in response to the governmental problem of how to manage emerging diseases. The grouping is tenuously held together by a shared commitment to the project of ‘pandemic preparedness’. However, as the controversy unfolds, it becomes clear that the main actors involved do not share a common understanding of the problem to be addressed by pandemic preparedness, and the assemblage threatens to decompose. At the center of the dispute is the question of how to assess the risks and benefits of research in field characterized by urgency and uncertainty.