BACKGROUND: Impaired pancreatic beta-cell responsiveness is associated with type 2 diabetes mellitus. Postprandial insulin deficiency is closely related with fasting plasma glucose, HbA1c and insulin responses to meals, but most studies examining postprandial beta-cell responsiveness have been limited by the small number of type 2 diabetic patients examined. The aim of this study was to evaluate fasting and postprandial insulin secretions in relation to the duration of diabetes, BMI and glycemic control in a large number of patients with variable disease durations. METHODS: We evaluated the fasting plasma glucose, insulin, C-peptide, HbA1c, BMI, postprandial 2 hour glucose, insulin and C-peptide in 1,170(male 662, female 508, age 54.6+/-1.6 years, duration of diabetes 5.2+/-6.3 years, BMI 25.4+/-3.3kg/m(2)) type 2 diabetic patients. The delta C-peptide, delta insulin, fasting(M0) and postprandial(M1) pancreatic beta-cell responsiveness were also calculated. The subjects were divided into three groups according to their duration of diabetes, BMI, and fasting and postprandial C-peptide levels. After adjusting for age, sex and BMI, the correlation of diabetes and HbA1c were correlated parameters. RESULTS: In the group of patients whose duration of diabetes was longer than 10 years, the BMI, fasting, postprandial and delta C-peptide, and M0 and M1 were significantly lower, but age, fasting and postprandial glucose, as well as HbA1c were significantly higher than those in the other groups. There were no significant differences in the fasting and postprandial glucose and HbA1c according to their fasting C-peptide tertiles. However, in the group of patients with the highest postprandial C-peptide tertile, the fasting and postprandial glucose and HbA1c were significantly lower than those in the other groups. The duration of diabetes, after adjustment of age, sex and BMI, was negatively correlated with the fasting, postprandial and delta C-peptide, M0 and M1, but was positively correlated with the fasting and postprandial 2 hour glucose and HbA1c. The HbA1c after adjustment of age, sex and BMI, was positively correlated with duration of diabetes, and fasting and postprandial glucose, but was negatively correlated with fasting postprandial and delta C-peptide, M0 and M1. CONCLUSION: Although the fasting and postprandial insulin secretions were decreased with duration of diabetes, the decrease in the postprandial insulin secretion was more prominent. The postprandial pancreatic responsiveness may be a more important factor in predicting glycemic control in Korean type 2 diabetic patients than the fasting pancreatic responsiveness.