Once considered potential sources of danger, generating industrial risks, companies are now viewed as indispensable partners in preparing risk responses. However, this shift raises the crucial question of the coordination between the various actors, especially as the literature - particularly on public-private partnerships (PPPs) and inter-organisational collaborations - highlights multiple potential obstacles. This article analyses the conditions and difficulties of this type of collaboration in preparing the response to a major collective risk - the threat of an influenza pandemic - by examining the relations between French public authorities and companies before and during the alert raised by an outbreak of A(H1N1). Shaped by responsibility and legitimacy issues, these relations are problematic and ambiguous, revealing a poorly designed framework which seems to be a source of difficulties rather than conducive to the effective handling of a pandemic threat. Ultimately, the study questions the desirability of a PPP in the specific context of risk management. This study is based on 30 interviews with public and private-sector actors together with the observation of conferences and the meetings of groups that exchange good practices between companies.