Colitis occurs spontaneously in the cottontop tamarin; it shares similar clinical, endoscopic and histological features with, and has a similar response to treatment as, human ulcerative colitis. An association between human ulcerative colitis and the presence of DNA from multiple herpesviruses (human herpesvirus 6 (HHV-6), cytomegalovirus (CMV) and Epstein-Barr virus (EBV) in the colon has been described. Intestinal herpesvirus infection may be involved in the pathogenesis of this condition. In a pilot study, coded full thickness colonic specimens from 27 cottontop tamarins were examined for the presence of HHV-6, CMV and EBV DNA using the nested polymerase chain reaction. The sections represented a spectrum of disease activity ranging from histologically normal bowel to severe colitis. A low prevalence of DNA from these viruses was found, which bore no relation to the presence of inflammation. Although these herpesviruses may have a pathogenetic role in human ulcerative colitis, they are not associated with colitis in this animal model.