Caucasian diabetic patients in Australian surveys showed a significant difference in the distribution of glyoxalase phenotypes. Insulin dependent diabetic patients with age of onset less than 40 years had a relative excess of glyoxalase homozygote 1-1 and a deficiency of types 2-1 and 2-2. Non-insulin dependent diabetic patients were not significantly different from non-diabetic subjects in the distribution of glyoxalase phenotypes. Insulin dependent diabetic patients without the complications of retinopathy or neuropathy also showed a significant excess of glyoxalase type 1-1 in relation to the control group. Genes controlling glyoxalase polymorphism appear to be associated with the variations of diabetes and its complications.