Pigment epithelium-derived factor (PEDF) is reported to play a protective role against diabetic vascular complications through its anti-oxidative properties. However, since a commercially available kit is not suitable for measurement of serum PEDF in humans, kinetics and regulation of serum PEDF are not known in these devastating disorders. Therefore, we developed a simple, specific and reliable method for measurement of serum PEDF in humans using a competitive enzyme-linked immunosorbent assay (ELISA) system. Assay linearity was shown intact with 50∼300-fold dilution of urea-pretreated serum by phosphate-buffered saline. The recovery ratio of added recombinant human PEDF in serum was 94.2 ± 1.7 %. Inter- and intra-assay coefficient of variations of the ELISA were 4.7 and 7.3 %, respectively. When we measured serum PEDF levels in a general population, PEDF levels were elevated in proportion to the accumulation of the number of the components of the metabolic syndrome. Further, the percent changes in serum levels of PEDF during 1-year observational periods were positively correlated with those of body mass index (BMI) in patients with type 2 diabetes. In addition, PEDF mRNA levels in cultured adipocytes were increased in parallel to the BMI values of subjects from which adipocytes were derived, especially in omental adipocytes. These observations suggest that PEDF is generated from adipose tissues and could be increased as a counter-system against vascular cell damage in humans. PEDF may be one of the useful biomarkers for vascular injury in high-risk patients.