Amylin is the major constituent of pancreatic islet amyloid whose accumulation characterizes patients with type 2 diabetes mellitus (T2DM). Although amylin is tightly linked with T2DM, in many cases, proamylin may be the more toxic species. As the precursor of amylin, however, the pathophysiological role of proamylin remains unknown. In this study, we investigate whether serum levels of proamylin or amylin or the proamylin/amylin ratios are different among normal subjects and patients with impaired glucose regulation (IGR) and T2DM. Totally 79 subjects were divided into three groups according to the results of oral glucose tolerance test (OGTT); they were T2DM group (32 cases), IGR group (23cases), and normal glucose tolerance (NGT) group (24cases). Serum levels of amylin and proamylin were measured with an enzyme-linked immunosorbent assay (ELISA). The relationships between serum levels of proamylin, amylin, their ratios and anthropometric and metabolic parameters were also analyzed. The serum levels of proamylin were significantly higher in patients with IGR and T2DM than in control subjects. The serum levels of proamylin were significantly associated with IGR and T2DM, with the odds ratios of 1.589 (95%CI, 1.228-2.055, P < 0.01) and 1.860 (95%CI, 1.342-2.587, P < 0.01), respectively. Both fasting serum levels of proamylin and proamylin/amylin ratios were found to correlate negatively with HOMA-B and DeltaI30/DeltaG30. Serum levels of proamylin, amylin, and their ratios were positively correlated with HOMA-IR. BMI and HOMA-B were independent related factors with serum levels of proamylin. Our results suggest that proamylin may play an important role in amyloid deposit in patients with IGR and T2DM.