We have studied HLA-A, -B, -C, -DR, and -DQ antigen frequencies in 63 Type 1 diabetic Arab patients resident in Kuwait. Both HLA-DR3 (relative risk (RR) = 5.80) and -DR4 (RR = 2.87) showed positive associations with Type I diabetes mellitus in these patients whilst -DR2 (RR 0.16) and -DR5 (RR = 0.15) were negatively associated. The strong positive association with both HLA-DR3 and -DR4 was confirmed in Non-Gulf Arabs (RR = 12.55 and 4.29, respectively) whereas the Gulf Arabs had a significant positive association with HLA-DR3 (RR = 4.41) only. The disease was negatively associated with HLA-DR2 (RR = 0.05) in Gulf Arab patients only and with HLA-DR5 (RR = 0.10) in Non-Gulf Arabs only. HLA-DRw52 and -DRw53 were increased in Non-Gulf Arabs only (RR = 3.14 and 4.63, respectively). In both groups there was strong association with HLA-DQ3 (Gulf, RR = 28.11; Non-Gulf, RR = 6.25). Amongst HLA-A, -B, and -C loci, there was a positive association with HLA-B8 (RR = 19.06).