Injection of sodium urate crystals into one ankle joint in the rat produces arthritis which is fully developed within 24 h. The time-course and dose-response of associated inflammation and sensory abnormalities are described. Following intra-articular sodium urate rats reduce the weight placed on the paw of the treated hind limb and develop a limp in their gait. The ankle swells and becomes more sensitive to pressure and passive movements. Touch, pressure and thermal stimuli applied to the foot distal to the treatment produce decreased responses, presumably because active flexion movements are noxious. Joint pathology is reflected by tissue oedema and the infiltration of polymorphonuclear leucocytes. However, there is no destruction or decrease in density of bone. It is proposed that this model of arthritis may have ethical and scientific advantages over adjuvant arthritis in the study of some aspects of the neural mechanisms of arthritis.