Wheat gluten was traditionally classified into gliadin and glutenin based upon solubility in aqueous alcohol. Gliadins were thought to be responsible for precipitating coeliac disease; glutenins were thought probably to be nontoxic. More recent classification, according to primary amino acid structure, reveals not only great heterogeneity but also similarities between different gliadin and glutenin proteins. Peptides derived from both groups are immunostimulatory in coeliac disease and it is highly probable that glutenin proteins are therefore toxic. Attempts to breed wheat with satisfactory baking properties tolerated by coeliac patients will be very difficult.