We have studied the frequency of HLA-DR, -MT, and -MB antigens in adult patients with coeliac disease and in a group of healthy controls, evaluating the strength of the observed associations by measuring the aetiologic fractions. Among the antigens significantly associated with coeliac disease, MB2 (DQw2) showed an aetiologic fraction higher than those of DR3 and DR7. Our results suggest that MB2, as associated more frequently than other specificities with a hypothetical disease predisposing gene, may play a role in the pathogenesis of coeliac disease. The significant association of DR3 and DR7 with coeliac disease may be ascribed to linkage disequilibrium of these antigens with MB2.