© 2001 by Taylor & Francis Group, LLC. The recent past has seen an increase in the study of mechanisms of visceral pain, principally due to the development of models that reasonably replicate human visceral pain. Prior to the characterization of such models, the chemically induced writhing model in mice or rats was considered to represent visceral pain. The chemical stimulus, injected into the peritoneal cavity, did not selectively activate the viscera, yielded false positives when used to screen potential analgesic drugs, and is, moreover, associated with a persistent stimulus from which the animal cannot escape. Current models of visceral pain utilize mechanical (e.g., distending) stimuli of controllable duration or chemical stimuli applied directly to relevant targets, thus permitting selectivity with respect to site and intensity of stimulation.