The harm benefit framework seems to have wide public support as a basis for making decisions about the use of animals in biomedical research. The present paper, which is the first of two papers that deal with the conceptual underpinning
of the harm-benefit analysis, focuses on the assessment of harms to animals. The goals of the 3Rs have gained wide acceptance over the 50 years since they were first proposed. However, there are controversial ethical issues hidden within the 3Rs principle. Five such hidden value conflicts are highlighted and it is argued that these conflicts challenge the idea that adherence to the 3Rs is bound to generate a wide public consensus. It is argued that underlying value differences will lead to conflicting interpretations of how to apply the 3Rs and thereby decide when and how to limit the harm imposed on animals.