Resistin is a peptide hormone encoded at the RSTN gene that since its detection in mice is considered to be an important link between obesity and insulin resistance. However, the study reports and especially the human data are contradictory and require further investigation. The purpose of this study was to evaluate three commercially available resistin ELISAs with different target epitopes (Phoenix, Belmont, CA, USA (PH); Biovendor, Brno, Czech Republic (BV); and Immundiagnostik, Bensheim, Germany (ID)) from a laboratory and clinical perspective. All three assays successfully passed the standardized technical validation procedure, with an inter- and intra-assay variability below 10% and 15%, respectively. They proved to be different with regard to calibration and reference ranges, which may be linked to the different antibody specificities. The clinical evaluation was performed with fasting serum samples from 78 patients with type 2 diabetes (43 female, 35 male, age (mean +/- SD, range): 67 +/- 10, (41-86) years; BMI: 29.2 +/- 4.2 (21.6-41.9) kg/m2). Insulin resistance was calculated from the fasting insulin and glucose values by means of the HOMA analysis. Intact proinsulin served as comparative laboratory marker for insulin resistance. The mean resistin values of patients without insulin resistance were slightly higher (PH: 9.5 +/- 2.8 ng/ml; BV: 4.1 +/- 4.0 ng/ml; ID: 3.8 +/- 9.0 ng/ml) than the mean values of the resistant patients (PH: 9.0 +/- 1.7 ng/ml, n.s.; BV: 3.8 +/- 1.3 ng/ml, n.s.; ID: 0.8 +/- 1.0 ng/ml, p<0.05). Intact proinsulin levels correlated well with the HOMA score values (r = 0.64, p<0.001). No correlation was seen between any of the resistin assays and any of the other clinical or laboratory observation parameters collected, such as BMI, age, disease duration, triglycerides, LDL, HDL, insulin, glucose, or intact proinsulin. In conclusion, the resistin assays showed good technical quality, but the diagnostic value remains still unclear. It may, however, be concluded from this study that at least in cross-sectional epidemiological investigations, fasting human resistin concentrations are not significantly correlating with any clinical measure for insulin resistance.