Gamma/delta T cells are increased in the gut epithelium of patients with coeliac disease compared with normal controls. The aim of this study was to determine whether the increase in gamma delta intraepithelial lymphocytes (IEL) is specific for coeliac disease, in which case it could be of diagnostic importance. Biopsies were obtained from children with no intestinal disease, coeliac disease, cow-milk-sensitive enteropathy/post-enteritis syndrome (CMSE PES) and miscellaneous other enteropathies (n = 67). Intraepithelial CD3+ and gamma delta T cells were identified in frozen sections using peroxidase immunohistochemistry. In normal biopsies there were 0-7 gamma delta IEL/100 cells in the epithelium. In untreated coeliac patients this increased to 9-22 gamma delta IEL/100 cells in the epithelium (P = 0.000004). Of 27 patients with morphologic intestinal damage which was not due to coeliac disease, four with CMSE/PES had gamma delta IEL/100 cells in the epithelium in the same range as the patients with coeliac disease. Of these, two had high densities of CD3+ IEL in the epithelium and were indistinguishable from patients with untreated coeliac disease. The other two could be excluded as possible coeliacs because their CD3+ IEL/100 epithelial cells were in the normal range. Thus an increase in gamma delta IEL is not specific for coeliac disease. However, enumeration of both of gamma delta IEL and CD3+ IEL densities will be useful in the exclusion of coeliac disease as a diagnosis in some children.