We performed a randomized crossover open comparative study to evaluate the efficacy and safety of voglibose and acarbose in 30 patients with type 2 diabetes who were not well controlled with diet therapy. There was no significant reduction of FBG with either voglibose or acarbose at 4 and 8 weeks after treatment. The 1 h postprandial blood glucose (PPBG) level was significantly decreased from 224.9+/-42.8 to 204.1+/-37.6 (P=0.005) and 206.1+/-38.9 mg/dl (P=0.038) after voglibose therapy at 4 and 8 weeks, respectively. Significant decrease was also obtained after acarbose treatment from 228.3+/-37.4 to 182.7+/-35.5 (P<0.001) and 186.6+/-36.1 mg/dl (P<0.001). The decrease of 1 h PPBG was associated with a significant fall of serum insulin concentration. HbA(1c) levels were also significantly decreased from 7.07+/-1.21 to 6.83+/-1.11 (P=0.017) and 6.79+/-1.33% (P=0.036) after voglibose and 6.98+/-0.98 to 6.70+/-1.04 (P<0.001) and 6.59+/-1.04% (P<0.001) after acarbose at 4 and 8 weeks. In contrast to voglibose, treatment with acarbose significantly decreased the 2 h PPBG at 4 and 8 weeks and the 2 h postprandial serum insulin concentration at 8 weeks. Adverse drug events were more commonly reported in acarbose-treated patients (P<0.05). Increased flatulence was observed in 56.7 and 90% of the patients taking voglibose and acarbose, respectively, while abdominal distention was noted in 10 and 16.7%. Significantly decreased body weights of 0.9 and 0.8 kg were recorded at 8 weeks after voglibose and acarbose therapy, respectively. We conclude that both voglibose (0.2 mg) and acarbose (100 mg) thrice daily significantly decreased HbA(1c), PPBG and postprandial insulin levels. At these dose levels, voglibose was associated with less gastrointestinal side effects and slightly less efficacy for postprandial glucose reduction.