Methods used to quantify the stress response in animals are vital tools in many areas of biology. Here we describe a new method of measuring the stress response, which provides rapid results and can be used in the field or laboratory. After a stressful event, we measure the capacity of circulating leukocytes to produce a respiratory burst in vitro in response to challenge by phorbol myristate acetate (PMA). During the respiratory burst leukocytes produce oxygen free radicals, and the level of production can be measured directly as chemiluminescence. When in vitro PMA-stimulated whole blood chemiluminescence is measured directly after a stressful event, we define the response as the leukocyte coping capacity (LCC). In an experiment badgers (Meles meles), which were caught as part of an on-going population study, were either transported to a central site prior to blood sampling or blood was collected at their site of capture. Transported animals had a significantly lower LCC and showed changes in leukocyte composition that were indicative of stress. We conclude that the stress of transport reduced LCC in badgers and that LCC serves as a quantitative measure of stress. Potential applications of this method are discussed. Experimental Physiology (2003) 88.4, 541-546.