The presence of antineutrophil cytoplasmic antibodies (ANCA) in serum has recently been shown to be a good disease marker for ulcerative colitis. An animal model of colitis expressing serum ANCA would allow prospective studies of the relationship between ANCA expression and development of colitis. The cotton-top tamarin model of spontaneous colitis was investigated for presence of ANCA to evaluate its potential as a model for the study of the immune response in human ulcerative colitis. Results show that cotton-top tamarin neutrophils have antigens recognized by immunoglobulin G (IgG) from the ANCA-positive serum of patients with ulcerative colitis. However, cotton-top tamarins do not generate serum IgG reactive to cotton-top tamarin or human neutrophils even when equal amounts of IgG are used for antigen detection. As new animal models of spontaneous and induced chronic colitis are developed, the presence of ANCA in serum, using the species' neutrophils, will be useful in relating the immune response of the model to that in human ulcerative colitis.