There are ethical and legal obligations to treat animals in a humane manner and to ensure high standards with respect to their husbandry and care, resulting in maximizing their well-being under the constraints of their use in science. The use of animals by humans is always associated with responsibility for the welfare of the animals concerned. However, when animals are used for research and subjected to procedures that may cause them pain, distress, suffering, and lasting harm, there are additional obligations to refine those techniques so as to cause only the minimum of pain and distress. It is important to separate the pain and distress that may be an unavoidable component of the research from that which is avoidable through, for example, better experimental technique or husbandry. Russell and Burch as long ago as 19591 referred to them as direct (necessary) and contingent (avoidable) inhumanities. They considered contingent inhumanity as being incidental or inadvertent (which may not be quite the same as avoidable), but it is generally agreed that any animal suffering not required to achieve the scientific objective can only confound the experiment being conducted. Many scientists are aware that severely stressed animals are not suitable for valid biomedical research, or as Russell and Burch wrote: “For some time it has been obvious to experimental biologists that severe pain, fear or in general distress in experimental animals, is an unmitigated nuisance in nearly all kinds of investigation… the effect of the treatment under study is utterly confused by the effects of the distress, and the animal ceases to be of the slightest use as a model of normal physiological function.” While this is not always true (e.g., gaining manual skills under a badly administered anesthetic), maintaining high standards of animals’ well-being is still an ethical, legal, and scientific obligation.