['To study the role of FABP4 in the plasma of type 2 diabetic (T2D) subjects with and without metabolic syndrome (MS) and the impact of thiazolidinedione (TZD) treatment.', 'FABP4 was analyzed in 274 individuals (169 T2D subjects and 105 controls). MS-T2D subjects had higher FABP4 levels than non-MS-T2D subjects and controls (53% and 76% increase, respectively, p<0.005). FABP4 levels in T2D subjects were positively correlated to the number of MS elements, obesity degree, adiponectin, triglycerides, lipoperoxides, C-reactive protein, age, systolic blood pressure and diabetes duration (p<0.05). Neither clinical or subclinical atherosclerosis, nor plasma levels of insulin, glucose or RBP4 were associated to FABP4. TZD-treated T2D subjects showed >30% higher FABP4 levels (p<0.05) than non-TZD-treated T2D. A subgroup study confirmed that TZD treatment prospectively increased FABP4 levels (p<0.05) along with an increase of peripheral blood mononuclear cell PPARgamma activity (p<0.05). Furthermore, in vitro studies showed that TZD treatment increased FABP4 mRNA, intracellular protein levels and extracellular secretion from human adipocytes.'] Is fatty acid binding protein 4 increased in metabolic syndrome and with thiazolidinedione treatment in diabetic patients?