Patient and public involvement in health research has been promoted by the United Kingdom's Department of Health and its research funding agencies for at least a decade. The policy rhetoric through which it is promoted is based on the idea that patients' experiential knowledge can be harnessed to improve the quality and relevance of health research. This paper uses the comparative case of post-colonial critiques of anthropology to propose ways of thinking about the implicit and explicit claims underpinning assumptions about experiential knowledge. It focuses on three areas of debate: insider knowledge and authenticity; objectivity/subjectivity; and ethical and political engagement.