The aim of this study was to investigate the relationship of alpha1-acid glycoprotein (AGP, orosomucoid), which is an acute-phase reactant, in patients with Type 1 (T1DM) and Type 2 diabetes mellitus (T2DM), with the metabolic parameters and complications of diabetes mellitus. A total of 119 diabetic patients (89 T2DM, 30 T1DM) and 33 healthy controls were included in the study. The mean AGP level in the diabetic group was not different from the control group (82.4 +/- 28.9 and 81.6 +/- 16.6 mg/dl, respectively), but it was higher in T2DM than in T1DM subjects (86.6 +/- 28.3 and 69.7 +/- 26.9, respectively). AGP plasma levels showed a significant correlation with age and body mass index (r = +0.348 and r = +0.296, respectively). AGP plasma levels resulted higher in obese diabetic patients (97.7 +/- 28.0) than in non-obese diabetic patients (77.6 +/- 28.7 mg/dl) and controls (81.6 +/- 16.6), and also higher in diabetic subjects with poor glycaemic control (85.1 +/- 33.3 mg/dl) than in diabetic subjects with optimal glycaemic control (79.5 +/- 23.1 mg/dl). A relationship between AGP and macro- and microvascular complications of diabetes mellitus was not found. In conclusion, inflammatory findings were more prominent in obese diabetic patients.