The prion protein is a cell surface glyco-protein expressed by neurones. Its function has remained elusive until it was recently shown to be a copper binding protein. There is now strong evidence that the prion protein has a role in normal brain copper metabolism. Prion protein expression alters copper uptake into cells and enhances copper incorporation into superoxide dismutase. Furthermore the prion protein itself can act as a superoxide dismutase. One aspect of prion disease is the conversion of functional prion protein into an aggregated amyloid. This conversion may alter the function of the prion protein or abolish it. These results suggest that prion disease may involve disturbance to brain copper homeostasis.