The expression of the 220,000 MW (p220) glycoprotein component of the leucocyte common antigen (LCA) family by intestinal mucosal lymphocytes was studied using the CD45R monoclonal antibody WR16. In normal intestine, a proportion of CD3+ mucosal T cells were WR16+ and this population resided predominantly in the mid-villus and crypt region of lamina propria. In the inflammatory infiltrates of both coeliac disease and Crohn's disease the CD3+, WR16+ population was markedly reduced. The monoclonal antibody UCHL1 identifies the 180,000 MW member of the LCA family and is expressed on T cells and in macrophages. CD3+ lymphocytes expressing this marker were widespread in normal lamina propria and epithelium. In contrast with WR16, UCHL1+ cells remained at a high level in coeliac disease and Crohn's disease. Our results support the view that loss of the p220 molecule occurs upon T-cell activation in inflammation.