This work reports the in vitro accelular behaviour of a glass ceramic (45P(2)O(5)-45CaO-5MgO-5K(2)O), which has significant potential for being used as an alloplastic bone graft. Experiments were carried out by immersing granule samples for a period up to 90 days in Tris-buffer solution at pH 7.4, in the presence and absence of a foetal bovine serum (FBS). The release of calcium, phosphorus, and potassium ions as well as the amount of protein adsorbed was followed by several techniques. The results obtained seem to indicate that the adsorption of proteins on the surface of the material, although causing an initial delay in the degradation, does not hamper the ionic exchange and therefore it is not a barrier for the degradation of the glass ceramic.