Differential expression of human leucocyte antigen (HLA) class II genes has been postulated to influence the risk of developing autoimmune disease. In this study, we investigated the relationship between the level of mRNA expression of DQA1 and DQB1 alleles in peripheral blood mononuclear cells and the influence of the alleles on susceptibility to type 1 diabetes (T1D). Transcripts from pairs of DQA1 and DQB1 alleles were quantified in 59 DQ-heterozygous individuals (29 patients with T1D and 30 healthy control subjects). Luciferase reporter gene assays were used to investigate the relative promoter activities of the alleles associated with high and low risk of disease. DQA1*0301 and the DQB1*06 group of alleles (*0601, *0602, *0603 and *0604) were generally overexpressed in comparison to other alleles. In contrast, mRNA for DQB1*0201/*0202 was generally less abundant than other DQB1 transcripts. These data correlated well with the relative promoter activities observed for the diabetes-associated alleles; the strongest promoters were those derived from DQA1*0301 and DQB1*0602, while a 700-bp fragment derived from the DQB1*0201 promoter showed the lowest activity of the DQB1 constructs. There was no simple correlation between the level of expression of specific DQ alleles and their influence on the risk of diabetes. The functional relevance of our findings and their implications for the pathogenesis of autoimmunity remain to be determined.