OBJECTIVE: To investigate the characteristics of the dysfunction of islet beta-cell in newly diagnosed type 2 diabetic patients. METHODS: Intravenous glucose tolerance test (IVGTT) was carried out on 352 newly diagnosed type 2 diabetic patients and 48 subjects with normal glucose tolerance (NGT) and then blood samples were collected 1, 2, 4, 6, and 10 minutes later to measure the plasma glucose and insulin to calculate the acute insulin response (AIR) and the area under the curve of insulin (AUC of insulin), homeostasis model assessment beta-cell (Homabeta), and Homa IR (insulin resistance). RESULTS: The median AIR of the type 2 diabetic patients was -33.7 pmol/L, significantly lower than that of the NGT subjects (6962.0 pmol/L, P < 0.001). The median AUC of the type 2 diabetic patients was 834.2 pmol/L, significantly lower than that of the NGT subjects (7934.7 pmol/L, P < 0.001). When the fasting plasma glucose (FPG) of the type 2 diabetic patients was above 7.0 mmol/L, the AIR value was remarkably reduced with a median level of 317.3 pmol/L, and then subsequently disappeared when the FPG was above 9.0 mmol/L. After adjustment of the insulin resistance assessed by HOMA IR, the Homabeta of the type 2 diabetic patients was reduced to be 30% that of the NGT subjects (3.7 +/- 0.9 vs 5.9 +/- 0.9, P < 0.001). Both the fasting proinsulin concentration and the ratio of fasting proinsulin to fasting insulin of the type 2 diabetic patients were significantly higher those of the NGT subjects (22.6 pmol/L +/- 14.7 pmol/L vs 11.5 pmol/L +/- 7.1 pmol/L, P < 0.001; and 30.1% +/- 20.5% vs. 12.1% +/- 9.6%, P < 0.001). CONCLUSION: The dysfunction of islet beta-cell in newly diagnosed type 2 diabetic patients is mainly represented by the disappearance of AIR and the evident decline of AUC and HOMA B, and the decrease of quality of insulin secretion.