Twenty one children with dermatitis herpetiformis were studied in an attempt to evaluate the response in the skin, in jejunal morphology, and in jejunal immunoglobulin containing cell counts to gluten elimination and subsequent gluten challenge. In all of the 15 patients whose jejunal biopsy was studied after the eventual gluten challenge the jejunal lesion had returned in 2.4 to 28 months. The numbers of IgA- and IgM-containing cells were similarly raised in primary and postchallenge biopsies. In the 13 patients whose skin improved during a gluten free diet and who were challenged with gluten the rash worsened and the dapsone/sulphapyridine requirement increased. The jejunal deterioration was equally marked in the six patients whose gluten challenge was stopped because of an intractable rash as it was in those who completed the preplanned challenge. The specimens of the former, however, had significantly more IgA-containing cells than specimens of the latter. The number of intraepithelial lymphocytes clearly reflected the degree of intestinal damage. IgA-containing cells proved to be the most sensitive indicator of an immune reaction taking place in the gut of these patients. Even in the two children with initially normal or nearly normal jejunal mucosa, the IgA cell counts in the jejunal lamina propria were markedly raised.