Dermatitis herpetiformis (DH) is a blistering autoimmune skin disease associated with a 95-100% incidence of the HLA class II antigen HLA-DQw2. Although the precise role of this antigen in the pathogenesis of DH is unclear, one theory proposes that patients with DH possess a molecularly unique subtype of the HLA-DQw2 antigen that causes immune abnormalities eventuating in the clinical manifestations of DH. To test this hypothesis, we performed DNA sequence analysis on the highly polymorphic HLA-DQB1 and HLA-DQA1 loci of eight patients with dermatitis herpetiformis. All DQB1 alleles sequenced were identical to the previously described HLA-DQB*0201 allele from HLA-DQw2 normal subjects. In addition, DQA1 alleles sequenced were identical to those alleles previously associated with HLA-DQw2 (DQA*0201, DQA*0501). These data document that although HLA-DQw2 appears to be a necessary element in the pathogenesis of DH, the development of DH is not dependent on the presence of a unique HLA-DQw2 antigen. HLA-DQ allelic typing by restriction fragment length polymorphism analysis of PCR-amplified HLA-DQA1 and HLA-DQB1 fragments was also performed in ten patients with DH to determine the allelic distribution among both HLA-DR3 (eight patients) and non-DR3 (two patients) DH patients. At the HLA-DQ beta chain locus, all patients possessed the DQB1*0201 allele. At the HLA-DQ alpha chain locus, all HLA-DR3 patients and one non-DR3 patient displayed a pattern consistent with the DQA1*0501 allele, whereas one non-DR3 patient displayed a pattern consistent with the DQA1*0201 allele. These data document that patients with DH do not express a unique HLA-DQw2 heterodimer, that the HLA-DQw2 molecules present in patients with DH have no DNA sequence differences from those found in normal HLA-DQw2 subjects and therefore that susceptibility to DH is not due to a unique HLA-DQw2 molecule.