Antigliadin antibodies in serum samples of 31 children with coeliac disease were measured by an enzyme-linked immunosorbent technique. In young patients (less than 2 years) tested before gluten withdrawal IgA antigliadin antibody levels were invariably above the levels of 36 controls. The titres fell rapidly when gluten was eliminated from the diet and rose on its reintroduction. The titres were not always greater than the control level in older untreated patients. IgA antigliadin antibodies seem to be a good marker of the immune reaction in the jejunum triggered by gluten. In 2 IgA-deficient patients gluten challenge caused an increase in IgM antigliadin antibodies, and at the same time the number of IgM-containing cells increased in the jejunal mucosa. Rising IgG antigliadin antibody levels after gluten elimination were seen in 6 patients, 5 of whom had very low complement C3 levels before gluten elimination.