This paper addresses the meanings of "ignorance" in the context of "don't know" responses to questionnaires. First, we consider some of the broader functions of questionnaires, suggesting that they reflect and mediate between particular types of institutions, respondents and society. We then unpack some of the meanings of "don't know" responses. Specifically, we argue that the "don't know" response is not merely a sign of deficit but, potentially, a potent political statement. Moreover, in relation to studies of the public understanding of science, it can be employed as a resource by people reflexively to express their identity through their relationship with science. Next we consider ignorance in the more expansive contexts of late modernity, which include concerns about the ambivalent role of science in general, the transgressive quality of biotechnology in particular and the impetus to narrate the self. Consideration of these factors, we argue, may be useful for further interrogation of the meanings of "don't know" responses.