We have previously proposed that intracrystalline proteins would increase intracellular proteolytic disruption and dissolution of calcium oxalate (CaOx) crystals. The aim of this investigation was to determine the effect of increasing concentrations of intracrystalline protein on the rate of CaOx crystal dissolution in Madin-Darby canine kidney (MDCKII) cells. Crystal matrix extract (CME) was isolated from urinary CaOx monohydrate (COM) crystals. Cold and ¹⁴C-oxalate-labelled COM crystals were precipitated from ultrafiltered (UF) urine containing 0-5mg/L CME. Crystal surface area was estimated from scanning electron micrographs and synchrotron X-ray diffraction was used to determine non-uniform strain and crystallite size. Radiolabelled crystals were added to MDCKII cells and crystal dissolution, expressed as radioactive label released into the medium, was measured. Increasing CME content did not significantly alter crystal surface area. However, non-uniform strain increased and crystallite size decreased in a dose-response manner, both reaching saturation at a CME concentration of 3mg/L and demonstrating unequivocally the inclusion of increasing quantities of proteins in the crystals. This was confirmed by Western blotting. Crystal dissolution also followed saturation kinetics, increasing proportionally with final CME concentration and reaching a plateau at a concentration of approximately 2mg/L. These findings were complemented by field emission scanning electron microscopy, which showed that crystal degradation also increased relative to CME concentration. Intracrystalline proteins enhance degradation and dissolution of CaOx crystals and thus may constitute a natural defence against urolithiasis. The findings have significant ramifications in biomineral metabolism and pathogenesis of renal stones.