Vaspin, designated as visceral adipose tissue-derived serpin, is a serpin whose expression is restricted to visceral adipose tissue. Vaspin seems to retain the serpin signature conformation fold consisting of three β-sheets and nine α-helices as well as a reactive loop site that interacts with its cognate serine protease unidentified hitherto. Vaspin is remarkably upregulated at high-fat high-sucrose (HFHS) diet and at multiple metabolic dysfunctions like obesity or insulin resistance. Administration of thiazolidinedione (TZD) caused a significant induction of serum vaspin in mice. These facts imply that upregulation of vaspin may be a compensatory response to antagonize the action of other unknown proteases upregulated in obesity or insulin resistance. Indeed, administration of recombinant vaspin to obese mice fed with HFHS chow improved glucose tolerance and insulin sensitivity. Vaspin seems to directly act on white adipose tissue. This assay is a sandwich Enzyme Linked-Immunosorbent Assay (ELISA) for quantitative determination of human vaspin in biological fluids. A monoclonal antibody specific for vaspin has been precoated onto the 96-well microtiter plate. Standards and samples are pipetted into the wells for binding to the coated antibody. After extensive washing to remove unbound compounds, vaspin is recognized by the addition of a purified polyclonal antibody specific for vaspin (Detection Antibody). After removal of excess polyclonal antibody, HRP conjugated anti-rabbit IgG (Detector) is added. Following a final washing, peroxidase activity is quantified using the substrate 3,3’,5,5’-tetramethylbenzidine (TMB). The intensity of the color reaction is measured at 450 nm after acidification and is directly proportional to the concentration of vaspin in the samples. The assay range is 0.016