Biomedical experimentation on animals is justified, researchers say, because of its enormous benefits to human being. Sure an imals die a nd suffer , but that is m orally insignificant since the benefits of research incalculably outweigh the evils. Although this utilitarian claim appears straightforward and uncontroversial, it is neither straightforw ard n ot uncontroversial. This defense of animal experimentation is like ly to succeed only by rejecting three widely held moral presumptions. W e identify those presumptions and explain their relevance to the justification of animal experimentation. We argue that even if non-human animals have con side rable less moral worth than humans, experimentation is justified only if its benefits are overwhelming. By building on arguments offered in earlier papers, we show that research ers c ann ot substantiate their claims of behalf of animal research. We conclude that there is currently no acceptable utilitarian defense of animal experimentation. Moreover, it is unlikely that they could be one. Since most apologists of animal experimentation rely on utilitarian justifications of their practice, it appears that biomedical experimentation on animals is not morally justified.