The purpose of the study was to determine the efficacy and tolerability of acarbose in Asian type 2 diabetic patients insufficiently controlled by insulin. Asian type 2 diabetic patients on stable insulin dosages were enrolled into a multinational, double-blind, placebo-controlled parallel arm study. After a 2-week screening phase, patients were randomly assigned to 50 mg acarbose t.i.d. or matching placebo for 6 weeks, followed by 100 mg acarbose t.i.d. or placebo for 12 weeks. The primary efficacy parameter was change from baseline in HbA(1c); secondary variables included the changes in fasting and postprandial blood glucose. After 18 weeks of treatment there was a difference in HbA(1c) levels between the two treatment groups (-0.69%, 95% CI (-1.18; -0.2), P=0.008) in favour of acarbose. Reductions in 1-h postprandial glucose levels from baseline to endpoint were observed with acarbose treatment (P=0.029). There were no differences in fasting blood glucose, total triglyceride and cholesterol between the two groups. Safety profiles were similar for both treatment arms except for the higher incidence of flatulence in the acarbose group (28.6% vs. 16.4% for placebo). Adjunctive acarbose therapy offers an efficacious and safe means for improvement of glycemic control in Asian type 2 diabetic patients insufficiently controlled by insulin.