Adiponectin, an adipose tissue-specific plasma protein, was recently revealed to have anti-inflammatory effects on the cellular components of vascular wall. Its plasma levels were significantly lower in men than in women and lower in human subjects with obesity, type 2 diabetes mellitus, or coronary artery disease. Therefore, it may provide a biological link between obesity and obesity-related disorders such as atherosclerosis, against which it may confer protection. In this study, we observed the changes of plasma adiponectin levels with body weight reduction among 22 obese patients who received gastric partition surgery. A 46% increase of mean plasma adiponectin level was accompanied by a 21% reduction in mean body mass index. The change in plasma adiponectin levels was significantly correlated with the changes in body mass index (r = -0.5, P = 0.01), waist (r = -0.4, P = 0.04) and hip (r = -0.6, P = 0.0007) circumferences, and steady state plasma glucose levels (r = -0.5, P = 0.04). In multivariate linear regression models, the increase in adiponectin as a dependent variable was significantly related to the decrease in hip circumference (beta = -0.16, P = 0.028), after adjusting body mass index and waist circumference. The change in steady state plasma glucose levels as a dependent variable was related to the increase of adiponectin with a marginal significance (beta = -0.92, P = 0.053), after adjusting body mass index and waist and hip circumferences. In conclusion, body weight reduction increased the plasma levels of a protective adipocytokine, adiponectin. In addition, the increase in plasma adiponectin despite the reduction of the only tissue of its own synthesis suggests that the expression of adiponectin is under feedback inhibition in obesity.