In an attempt to confirm the existence of latent coeliac disease--dose-related gluten-sensitive enteropathy--we have increased dietary gluten by 20 g daily for 2 weeks, in 6 healthy adults and 11 patients with dermatitis herpetiformis (DH). Six of the DH patients had entirely normal jejunal morphology on a normal diet. Jejunal biopsy specimens were taken before and at the end of the study. Measurements of crypts, villi, and crypt mitoses were made on microdissected specimens; disaccharidases were assayed, and intraepithelial lymphocyte counts performed. In one of the six adult volunteers, gluten loading produced diarrhoea and jejunal biopsy abnormalities. Five DH patients on a gluten-free diet had deterioration of biopsy pathology after the gluten challenge. Features suggestive of a latent gluten-sensitive enteropathy were found in one of the other six DH patients; he developed disaccharidase deficiencies and villus atrophy when 20 g gluten was added to his usual gluten-containing diet. This study supports previous suggestions that a gluten-sensitive enteropathy may be latent and dose-related.