Caeruloplasmin is a copper binding plasma glycoprotein consisting of a single polypeptide chain. It has a molecular weight of 132kDa and occurs in plasma at a concentration of 150-500 mg/L. Although the physiological functions of Caeruloplasmin are not fully understood it is implicated in a number of possible functions. 95% of plasma copper is bound to Caeruloplasmin, implying some involvement in copper transport. Caeruloplasmin has been described as both an oxidant and an antioxidant, its exact role or roles in this respect are not clear. Plasma levels of Caeruloplasmin are elevated after inflammation and trauma and it is therefore classified as an acute phase protein. The measurement of Caeruloplasmin in plasma is useful in the diagnosis of Wilson’s disease, where levels are greatly reduced. Caeruloplasmin is extremely labile in plasma and rapidly degrades to 115kDa and 19kDa fragments. The age of plasma samples should therefore be taken into account when interpreting immunological analysis of caeruloplasmin.