Refinement of research techniques using animals will lead to less animal distress and, at the same time, will usually lead to higher quality and more robust data. For example, acclimation of laboratory animals to handling and experimental procedures will produce not only an animal that is easier to handle but also one that reacts to the experimental stimulus rather than to the handler. Even when the animal is acclimated to handling, handling or anesthesia can cause marked changes to commonly measured biological parameters such as serum hormone and tissue metabolite levels. Standard animal housing systems are also stressful to the animals. One research report, for example, found that mice in conventional facilities had plasma corticosterone values of 150-500 ng/ml compared to values below 35 ng/ml from mice kept in special "low-stress" housing. However, assessment of stress in animal research is not easy and few technicians or research scientists are good judges of moderate stress. Investigators in the United Kingdom have recently published a report on a new technique that might allow more objective assessment of discomfort in laboratory rats and mice. The amount of exploratory behavior in treated and control animals can be used for developing a Disturbance Index (DI). The DI is a measure of the extent to which a procedure or treatment causes a departure from normal behavior. The initial data using the DI indicate that it could be a promising approach for assessing animal well-being (or the lack of it).