Haptoglobin, an "acute phase" protein, has different functions, which display genetic polymorphism. The complex of haptoglobin with haemoglobin is metabolized in the heptic reticuloendothelial system. Biosynthesis of haptoglobin occurs not only in the liver, but also in adipose tissue and in lung; providing antioxidant and antimicrobial activity. Changes in the measured concentrations of haptoglobin in serum may help to assess the disease status of patients with inflammations, infections, malignancy etc. (increases) as well as in haemolytic conditions (decreases). Haptoglobin plays a role in stimulation of angiogenesis and has highly potent cholesterolcrystallization-promoting activity. Probably the most important biological function of haptoglobin consists in the host defence responses to infection and inflammation, acting as a natural antagonist for receptor-ligand activation of the immune system.