This paper addresses several questions related to the nature, production, and use of animal-human (a-h) chimeras. At the heart of the issue is whether certain types of a-h chimeras should be brought into existence, and, if they are, how we should treat such creatures. In our current research environment, we recognize a dichotomy between research involving nonhuman animal subjects and research involving human subjects, and the classification of a research protocol into one of these categories will trigger different ethical standards (...) as to the moral permissibility of the research in question. Are a-h chimeras entitled to the more restrictive and protective ethical standards applied to human research subjects? We elucidate an Aristotelian-Thomistic metaphysical framework in which to argue how such chimeras ought to be defined ontologically. We then examine when the creation of, and experimentation upon, certain types of a-h chimeras may be morally permissible. (shrink)