A case-control study to investigate whether the aldose reductase (AC)(n) dinucleotide polymorphism (termed 5'-ALR2 polymorphism) is useful as a genetic marker for risk of microvascular complications among Caucasians Type 1 diabetic patients in Australia is reported. This marker was amplified from patient genomic DNA and then fractionated in 5% formamide-urea gels. A total of nine alleles was observed with Z, Z-2 and Z+2 being the major alleles. The distribution of alleles was comparable in diabetic subjects with diabetes and microvascular complications, diabetes without complications and normal non-diabetic control subjects. Similarly, when the distribution of alleles was examined in the patients subcategorized according to the presence of diabetic nephropathy or diabetic neuropathy, no significant association was observed. While the size of the study makes it impossible to exclude a weak linkage, it is concluded that the 5'-ALR2 polymorphism is not useful as a genetic marker for susceptibility to diabetic microvascular complications in Caucasian Type 1 diabetic patients.