Adiponectin is a plasma protein derived from adipose tissue, which we discovered from a human adipose cDNA project. Adiponectin exists in circulating plasma at concentrations ranging from 4 to 30 microg/mL, which is much higher than the concentrations of various other hormones and cytokines. Adiponectin has a sticky nature, binding to collagen I, III, and V, which are present in vascular intima. Adiponectin exhibits various antiatherogenic effects on vascular cells, suppressing the expression of adhesion molecules in vascular endothelial cells, proliferation of smooth muscle cells, and cholesteryl-ester accumulation in macrophages. However, its plasma levels are low in subjects with excess intra-abdominal fat. Adiponectin also has antidiabetic properties, and plasma adiponectin levels correlate positively with insulin sensitivity. Several clinical studies have demonstrated that hypoadiponectinemia is a risk factor for new-onset diabetes. Recent studies suggest that hypoadiponectinemia may partly contribute to the development of salt-sensitive hypertension and hypertensive heart failure, and can be also a risk factor for overnutrition-related cancers such as breast, colon, uterine, and prostate cancers. Hypoadiponectinemia might be at least in part the molecular basis of various diseases associated with overnutrition.