Lucigenin-enhanced chemiluminescence can be measured in 100μl samples of whole, unseparated mouse blood. A procedure for doing so is here described in detail, using a standard clinical luminometer. The assay measures the TPA-induced oxidative burst from granulocytes and macrophages, which is believed to depend on the overall level of inflammation in the body. It is here applied to mice suffering from type II collagen-induced arthritis, and its relation to overt disease symptoms (the arthritis score) is characterised during the course of the disease. A correlation between the assay and the arthritis score is found at the height of the disease (r = 0.42, p =. 039), but not at early or very late time points, although there is a strong hint that the results of an early assay may predict the subsequent disease course. The assay provides a rapid, convenient, quantitative and economical method of assessing disease activity, which can be carried out repeatedly on the same individual. It should be applicable in other mouse models of chronic inflammatory disease. It may find application for rapid screening of novel anti-rheumatic drugs and treatments.