Combinations of insulin and oral antidiabetic drugs (OAD) are often prescribed instead of insulin alone. In this study, the effects of insulin glargine (IG) in combination with repaglinide or acarbose on glycemic parameters were investigated. Obese Type 2 diabetic patients with fasting blood glucose (FBG) levels >= mmol/l and hemoglobin glycated (A1C) >= 9% under maximal CAD combination therapy were enrolled. Previous therapies were discontinued, and patients were randomized into 2 groups. The combinations of IG and repaglinide were administered to group 1, and of IG and acarbose to group 2 for 13 weeks. Twenty Patients in group 1 and 18 patients in group 2 completed the study. A1C levels were significantly decreased from 10.9 +/- 1.4% to 7.7 +/- 1.1% in group 1 and 11.0 +/- 1.4% to 8.1 +/- 1.4% in group 2. FBG levels were significantly decreased from 11.9 +/- 2.7 to 7.1 +/- 2.3 mmol/l in group 1 and 11.1 +/- 2.5 to 6.8 +/- 1.4 mmol/l in group 2. Post-prandial glucose levels were significantly decreased from 15.3 +/- 3.8 to 10.3 +/- 3.0 mmol/l in group 1 and 14.0 +/- 3.1 to 8.9 +/- 2.2 mmol/l in group 2. Intergroup comparisons indicated no significant differences. More weight gain was detected in group 1, compared to the baseline. Syptomatic hypoglycemia incidence was similar in both groups. Severe hypoglycemic attacks were seen in two patients in group 1. Flatulance incidence was higher in acarbose group. Conclusively, repaglinide and acarbose were equally effective when combined with IG for obese Type 2 diabetic patients controlled inadequately with OAD alone. Furthermore, acarbose seems to have advantages over repaglinide concerning weight gain and severe hypoglycemic attacks.