We studied the numbers of T-cell receptor α/β- and γ/δ-bearing lymphocytes in 27 jejunal specimens from 19 celiac patients, 27 rectal and colonic specimens from 14 ulcerative colitis patients and four patients with Crohn's disease, and 24 control specimens. MAb and a three-layer peroxidase staining method were used. Only low numbers of γ/δ+ cells were seen in normal jejunum and rectum of controls, as well as in the specimens of patients with inflammatory bowel diseases. In the lamina propria of celiac patients, the mean number of γ/δ+ cells was significantly higher than in the controls before treatment, during gluten-free diet, and after the gluten challenge. Within the jejunal epithelium, the number of γ/δ+ cells was elevated before and during gluten elimination and after the challenge test. The absolute number of intraepithelial γ/δ+ cells remained constant during gluten elimination and provocation. We infer that the constantly elevated population of γ/δ+ T cells in the epithelium of celiac patients may play an important role in the pathogenesis of celiac disease.