We investigated the expression of leptin and leptin receptor (OB-R) at the protein level by flow cytometry and also quantified by real-time reverse transcriptase-polymerase chain reaction (RT-PCR) the two major leptin receptor isoforms (OB-Rl, OB-Rs) in peripheral blood mononuclear cells (PBMCs) of patients with hepatitis B (HBV; n = 31), hepatitis C (HCV; n = 34), and nonviral liver disease (n = 25), and healthy controls (n = 36), as well as in liver tissues of HBV (n = 8), HCV (n = 7), and healthy individuals (n = 6).