Public health authorities across the globe have reassured members of the public that they are vigilant to the threat of bird flu’s pandemic potential. But they have also made requests of members of the public to play their own role in vigilance mechanisms, most notably requiring poultry farmers to adopt biosecurity measures at their farms. When should vigilance be practised, and under what circumstances are vigilance requests of publics ethically justified? This paper begins by considering the sociological literature on vigilance in public health. In doing so, it discusses the relationship between vigilance, surveillance and other concepts in public health and establishes the need for moral reflection on vigilance as a distinct category in public health ethics. It then considers the requests for vigilance made to poultry farmers during bird flu as an ethical case study, before ending by providing a series of ethical questions that must be answered by government health authorities considering instituting systems of vigilance and making vigilance requests of publics.