Evidence for autoimmunity in diarrhoeal disease is reviewed. Firstly, coeliac disease (CD) is considered. The incidence of tissue-reactive autoantibodies in both adults and children with CD (68% and 65%, respectively) is higher than the incidence of these autoantibodies in controls (6% in normal adults, and 14% and 9% in disease controls drawn respectively from adult and child populations). The R1 antireticulin antibody, when present, was found to disappear after several weeks on a gluten-free diet, but in contrast, other autoantibodies persisted. Secondly, a case is argued for a new disease category, namely "autoimmune enteropathy." Seven cases are reviewed in which patients presented with protracted diarrhoea, a small intestinal enteropathy which failed to heal during periods of total parenteral nutrition, and evidence of a predisposition to autoimmunity (namely, the presence of high titre autoantibodies including one specific for gut epithelium, and/or the presence of associated diseases regarded to be autoimmune). Thirdly, evidence for autoimmunity in inflammatory bowel disease is reviewed and includes discussion of serum goblet cell antibodies and of circulating T cells which participate in antibody-dependent cellular cytotoxicity in vitro using colonic epithelial cells as targets. Finally, an unusual child is described who presented with chronic diarrhoea and a flat small intestinal mucosa, who responded to gluten withdrawal but who later relapsed spontaneously during a strict gluten-free diet. Her mucosa healed only after a period of total parenteral nutrition and treatment with oral steroids. This child's enteropathy was also associated with thyrotoxicosis and a microscopic colitis.