Jejunal biopsies from 16 treated coeliac disease patients and from nine controls were cultured with and without a peptic-tryptic digest of gliadin. Cultures with a peptic-tryptic digest of maize prolamins were also undertaken. Frozen sections of baseline and cultured mucosa were stained by immunofluorescence with an anti-HLA-DR monoclonal antibody. Before culture the villous epithelium from both controls and treated coeliac disease expressed DR molecules while the crypt epithelium did not. When biopsies from treated coeliac disease were cultured with gliadin the expression of DR was enhanced in the crypt epithelium in eight of 14 cultures and in 11 of 14 was reduced or absent on the villous epithelium. No change was observed in control cultures. We conclude that gliadin is capable of inducing HLA-DR on the crypt epithelium of in vitro cultured coeliac disease mucosa, providing indirect evidence that gliadin may activate cell mediated immune mechanisms within the small bowel mucosa. This model could prove useful in identifying the immunogenic sequence(s) of gliadins and related prolamins.