Animal research remains a deeply controversial topic in biomedical science. While a vast amount has been written about the ethical status of laboratory animals, far less academic attention has been devoted to the public and, more specifically, to public opinion. Rather than what the public think, this article considers the role of ‘public opinion’. It draws on a recent empirical study which involved interviews with laboratory scientists who use animals in their research, and with other UK stakeholders. The first section of the paper demonstrates that public opinion has become a kind of resource in the animal research debate. Public opinion polls, in particular, are frequently cited. The second section explores this further and argues that, for all sides, appealing to public opinion is a key way to show legitimacy. Finally, the paper shifts gear to consider whether public opinion should matter, both for ethical reasoning and for science policy.