In the long history of moral theory, non-human animals—hereafter, just animals—have often been neglected entirely or have been relegated to some secondary status. Since its emergence in the early 19th century, utilitarianism has made a difference in that respect by focusing upon happiness or well-being (and their contraries) rather than upon the beings who suffer or enjoy. Inevitably, that has meant that human relations to and use of other animals have appeared in a different light. Some cases have seemed easy: once admit that the interests of animals matter and there can be little hesitation in condemning their cruel treatment. Among the more difficult cases has been the bearing of utilitarianism upon the use of animals in various kinds of research where, though the animals might suffer, there were believed to be prospects of great human benefit and where no cruel or malicious motives need be involved. What I shall provide in the current paper is an extended discussion of the bearing of utilitarianism upon practices of animal research. Since such practices have attracted both utilitarian criticism and defense, this will require the examination of arguments on both sides, including consideration of the human benefits, the animal costs, and the ways in which the one can be weighed against the other.