Circulating leukocyte-platelet heterophilic aggregates produce procoagulant, oxidative and mitogenic substances, and can cause microembolism in capillaries as well as acute arterial thrombosis. Our aim was to determine if there was any difference in the number of circulating heterophilic aggregates between diabetic patients and controls, if the formation of aggregates correlated with the actual HgbA1c level, duration of diabetes and postprandial rise in serum glucose level, with different vascular complications and whether decreasing postprandial serum glucose had any effect on heterophilic aggregate formation. The number of circulating heterophilic aggregates was measured in 90 diabetic patients (Type 1, 29; Type 2, 61) and in 23 control subjects by a flow-cytometric assay, and the result was given as percentage of the respective leukocyte subsets. There was no significant difference in lymphocyte-platelet and neutrophil-platelet aggregate number in patients and controls; however, there was a significant difference in the percentage of monocyte-platelet aggregates between the diabetic and control group (Type 1, 43.0 +/- 17.8; Type 2, 34.9 +/- 12.5; control, 24.6 +/- 8.2; P < 0.01 and P < 0.5, respectively). Patients with proliferative retinopathy and nephropathy showed the highest number of monocyte-platelet aggregates. No significant correlation was, however, found with HgbA1c. In Type 2 diabetes a non-significant, but remarkable, tendency between elevation of postprandial serum glucose levels and platelet-monocyte aggregate formation was observed and acarbose seemed to be effective in decreasing both. This study provides further support that heterophilic aggregates might have role in the pathogenesis of diabetic vascular complications.