This article presents the ethical issues in animal research using a combined approach of ethical theory and analysis of scientific findings with bearing on the ethical analysis. The article opens with a general discussion of the moral acceptability of animal use in research. The use of animals in research is analyzed from the viewpoint of three distinct ethical approaches: contractarianism, utilitarianism, and animal rights view. On a contractarian view, research on animals is only an ethical issue to the extent that other humans as parties to the social contract care about how research animals are faring. From the utilitarian perspective, the use of sentient animals in research that may harm them is an ethical issue, but harm done to animals can be balanced by benefit generated for humans and other animals. The animal rights view, when thoroughgoing, is abolitionist as regards the use of animals in science (as in any other human use that is not also in the animals’ best interest). These views are not compatible, and since all three views in more or less pure form are found in modern Western societies, use of animals for research is bound to cause controversy. However, there may be room for some kind of compromise where adherents of each view compromise on some points. The ethical basis for the mainstream view of the use of animals in research is analyzed in this light. In the second part of the article, scientific information about the use of animals in research (and in particular the harm and benefit of such use) is analyzed in the light of ethical questions that seem to be pertinent against the background of a mainstream compromise view.