Increased density of gamma/delta T cell receptor (TCR)+ intraepithelial lymphocytes is the only characteristic in the jejunum of patients with coeliac disease and dermatitis herpetiformis which is not normalized on a gluten-free diet. We explored the age-dependent changes in intraepithelial gamma/delta and alpha/beta TCR+ cells from 137 biopsies from patients with coeliac disease and dermatitis herpetiformis and from controls. Biopsy specimens from 100 patients with coeliac disease and dermatitis herpetiformis and from 37 controls were studied with an immunohistochemical method using MoAbs to T cell receptors and peroxidase staining. An increase in the density of intraepithelial gamma/delta T cells above the mean +2 s.d. of the density in controls was present in 97 of 100 specimens from patients with coeliac disease and dermatitis herpetiformis. The density of gamma/delta+ cells of patients with coeliac disease and dermatitis herpetiformis on a normal gluten-containing diet showed a positive correlation with age (r = 0.45, P < 0.0001). In controls, the density of gamma/delta+ cells remained low throughout the age-range studies, from age 0.6-57 years. In controls, alpha/beta+ cells increased with age (r = 0.57, P < 0.001). The increase in density of intraepithelial lymphocytes with age is in agreement with their thymus-independent character and local proliferation.