There appears to be an obvious difference in the susceptibility to diabetic microangiopathy among Type 2 diabetic (T2DM) patients. We examined the hypothesis that aldose reductase (AR) messenger ribonucleic acid (mRNA) expression may be enhanced in diabetic patients susceptible to diabetic microangiopathy by measuring AR mRNA expression in the polymorphonuclear leukocytes (PMNs) obtained from T2DM patients. The AR mRNA and beta-actin mRNA expressions were measured by reverse transcription-polymerase chain reaction method. The relative AR mRNA expression to beta-actin mRNA expression significantly increased in the PMNs of T2DM patients, compared to normal healthy controls. The relative AR mRNA expression tended to increase with an increase of glycosylated haemoglobin A1c (HbA1c) levels. The patients who showed both progressive diabetic retinopathy and diabetic neuropathy within 10 years after the diagnosis of T2DM (Group I) showed significantly 1.6 times higher AR mRNA expressions than those who have not shown both complications over 10 years after diagnosis (Group II), in spite of no obvious difference in glycaemic control between both groups. The present data indicate that the AR mRNA expression increased in the PMNs of T2DM patients and there is an obvious difference in the PMNs AR mRNA expression between T2DM patients susceptible and relatively resistant to the development of diabetic microangiopathy.