Tissue typing (HLA-A, -B and -DR) was carried out on 92 patients with coeliac disease (CD) and on a further 71 first degree relatives of 13 of these patients. Results of antigen frequencies in unrelated patients and segregation analysis in families shows that HLA-DR3 but not HLA-DR7 is positively associated with CD. Haplotype and sib-pair data from these coeliac families suggest that with all of them, genetic susceptibility to CD lies in the HLA region of the sixth chromosome. In families where the coeliac proband has HLA-DR3, the relative risk to siblings who also have this antigen is increased 35 times.