BACKGROUND Inflammation and the metabolic syndrome (MetS) are important risk factors in cardiovascular disease. There is accumulating evidence that decreased adiponectin levels are associated with MetS. Recently, it was shown that adiponectin induces the expression of a potent anti-inflammatory cytokine, interleukin (IL)-10, in vitro. The aim of this study is to investigate the association of IL-10 levels with other pro-inflammatory and anti-inflammatory factors including adiponectin levels in vivo. METHODS AND RESULTS MetS components were assessed in 117 drug-naïve middle-aged men. Serum levels of high-sensitive C-reactive protein (hs-CRP), IL-6, adiponectin, IL-10 and tumor necrosis factor-alpha (TNF-alpha) were measured in these subjects. A significant decrease in adiponectin (5.15+/-1.79 microg/ml vs 6.87+/-3.55 microg/ml, p<0.02) and an increase in IL-6 (1.50+/-1.50 pg/ml vs 1.06+/-0.78 pg/ml, p<0.05) levels were associated with MetS. The serum IL-10 level exhibited a significant positive correlation with IL-6, hs-CRP, and TNF-alpha levels, but not with adiponectin in healthy individuals. However, IL-10 exhibited a significant correlation with adiponectin, especially in the subjects with MetS. CONCLUSIONS Serum IL-10 levels correlated with inflammatory proteins, but not with adiponectin. However, IL-10 positively associated with adiponectin especially in the subjects with MetS. IL-10 might be involved in the inflammatory network of MetS in relation to adiponectin.