There is considerable evidence that the prion protein binds copper. However, there have also been suggestions that PrP binds manganese. We used isothermal titration calorimetry to identify the manganese binding sites in wild-type mouse PrP. The protein showed two manganese binding sites with affinities that would bind manganese at concentrations of 63 M and 200 M at pH5.5. This indicates that PrP binds manganese with similar affinity to other know manganese binding proteins. Further study indicated that the main manganese binding site is associated with H95 in the so called “5th site” normally associated with copper binding. Additionally, it was shown that occupancy by copper does not prevent manganese binding. Under these conditions, manganese binding results in an altered conformation of PrP, displacement of copper and altered redox chemistry of the metal-protein complex. Cyclic voltammetric measurements suggest complex redox chemistry involving Mn bound to PrP while Cu bound PrP is able to undergo fully reversible electron cycling. Additionally, Mn binding to PrP converts it to a form able to catalyse aggregation of metal free PrP. These results further support the notion that manganese binding could cause conformation change in PrP and trigger changes in the protein similar to those associated with prion disease.