Activated T cells can be visualized in the intestinal lamina propria in a number of gastrointestinal diseases including food-sensitive enteropathy (coeliac disease), inflammatory bowel disease and intractable diarrhoea of infancy. Experimental studies have shown that T-cell activation in human intestinal lamina propria in vitro produces an increase in crypt cell proliferation, villous atrophy, increased HLA-DR expression on enterocytes, increased intra-epithelial lymphocyte numbers, and phenotypically, macrophage activation. All of these features are seen in human gastrointestinal disorders and it is proposed that T-cell activation to wheat (in coeliac disease), milk (cows' milk-sensitive enteropathy), and unidentified luminal antigens (Crohn's disease) plays a primary role in the pathogenesis of these disorders.