Leptin plays an important role for the regulation of food intake, energy expenditure and glucose control. The aim of this study was to study the effect of surgery on circulating levels of human leptin in a human elective surgery model. A prospective observational study was conducted. Blood sampling was carried out prior to surgery and four and thirty days after elective surgery, respectively. Patients undergoing orthopedic surgery (n=29) and coronary bypass patients (n=21) were included in the study. Serum leptin levels were measured using sandwich ELISA. C-reactive protein (CRP) was analyzed by turbidimetry.