Fat is now considered as an endocrine organ that produces a lot of molecules having biological activity, called adipocytokines. Among these, adiponectin, a 247 amino acid protein produced abundantly and specifically by adipose tissue, besides its effects on glucose metabolism, plays important protective function against cardiovascular diseases. Circulating levels lower than those of healthy control subjects have found to be associated to conditions such as obesity, diabetes and cardiovascular diseases. In animal experimental models, administration of adiponectin has been shown to have beneficial effects against the development of obesity-related vascular diseases, including atherosclerosis. In humans, circulating levels can be raised by life style modification (weight loss or exercise training) or pharmacological treatments. Adiponectin is present in the human plasma in different isoforms: a large multimeric structure of high molecular weight and in a trimer and examer form, whereas the monomeric form is found only in the adipose tissue. The biological activities of the different multimers are not yet fully known, although the different isoforms appear to have different functional importance following the different diseases. This paper reports the main biological features of adiponectin in order to highlight its possible role as diagnostic/prognostic marker in cardiovascular diseases. Particular attention is paid to practical considerations relative to the analytical determination of this protein in humans.