Genes in the HLA complex are associated with susceptibility to develop insulin-dependent diabetes mellitus (IDDM). Several studies, from different populations, have demonstrated strong associations between particular DR and DQ alleles and disease susceptibility or protection. Whether also particular DP alleles may independently contribute is more controversial. Some studies have found a greater frequency of DPB1*0301 among IDDM patients compared to controls, apparently independently of linkage disequilibrium with high risk DR and DQ alleles. To address this question in an ethnically homogeneous population (Norwegian), we have DPA1 and DPB1 genotyped 237 IDDM patients and 287 DRB1-DQA1-DQB1 matched controls, carrying high risk DR3/4 or DR4/4 genotypes. We were unable to detect any significant independent associations between DP alleles and IDDM susceptibility or protection in this population. Thus, our results do not support previous reports on an independent association between some DP alleles and susceptibility to develop IDDM.