Animal experimentation is one of the most controversial areas of debate on animal rights. Biomedical research is at the hard edge of these debates: it throws up fundamental questions of moral value—of whether human life is more important than that of animals. Much experimentation is defended by its apparent success in terms of increasing medical knowledge. This study investigates whether biomedical research using animals is, in fact, scientifically justified. The authors show that in scientific terms—using the models that scientists themselves use—these claims are exaggerated, or even false. They argue that we need to reassess our use of animals and, indeed, rethink the standard positions in the debate. Their analysis reveals why research using animals might be a source of hypotheses about human biomedical phenomena, yet would never prove or establish anything about this phenomena.