The frequency distribution of alleles controlled by the factor B (Bf) and glyoxalase genes that are found close to the HLA system on chromosome 6 was studied in 170 insulin-dependent diabetic patients. The data were compared with those for HLA-A, -B and -DR antigens and were related to age of onset of diabetes. All the diabetics were ketosis prone and on permanent insulin therapy. A significant excess of BfF1 was seen in the diabetic patients (p less than 10(-4]. Glyoxalase frequency distribution showed no significant deviation from controls, whereas HLA-DR3 (p less than 10(-4] HLA-DR4 (p less than 10(-4] were increased. Breakdown of data by age of diagnosis of disease showed no increase in the frequency of BfF1 and GLO1-2 but an increase of HLA DR3 and DR4 in patients with early onset diabetes. The findings of the study are consistent with data reported by others investigators and support the notion that one or more genes mapping close to the HLA A. B and DR and to the Bf loci confer susceptibility to insulin dependent diabetes.