Human alpha 2-macroglobulin, a plasma glycoprotein, traps and inhibits proteolytic enzymes which participate in inflammation and homeostasis. There is no doubt about the significant role of alpha 2-macroglobulin in immunoregulatory processes. The aim of the present study was to investigate the levels of alpha 2-macroglobulin in patients with diabetes mellitus and to investigate whether an association exists between alpha 2-macroglobulin level and the type of diabetes (type I or type II) or alpha 2-macroglobulin and diabetic complications. The patient population consisted of 48 patients with diabetes mellitus type I (average age 36.5 years) and 50 patients with diabetes type II (average age 55.3 years). Patients were divided into three groups according to the presence of complications (group I--patients without complications, group II--patients with diabetic retinopathy, group III--patients with several complications). alpha 2-macroglobulin was determined by electroimmunoassay according to Laurell. alpha 2-macroglobulin levels were significantly raised in group of diabetics type I (3190 mg/l vs. 1880 mg/l). In the group of diabetics type II alpha 2-macroglobulin levels are within the normal range (2030 mg/l vs. 1880 mg/l). After dividing of diabetics according to the presence of diabetic complications, alpha 2-macroglobulin levels in patients with diabetic complications were significantly higher than in the group of diabetics without complications (3180 mg/l vs. 2040 mg/l). The possible explanations of elevated alpha 2-macroglobulin levels in diabetics and possible participation of elevated a2-macroglobulin in the development of diabetic angiopathy are discussed. (Fig. 2, Ref. 14.)