Human urine is supersaturated with respect to calcium salts especially calcium oxalate which is the major mineral phase of urinary stones. Inhibitors of crystallization prevent renal calcification in urine. Small molecular weight components account for 20% of total inhibitory activity of urine. Macromolecular inhibitors (molecular weight greater than 10 kDa) are more powerful. Recently, several macromolecules have been identified in urine, in urinary stones and in the kidney: Nephrocalcin, Tamm-Horsfall protein, Uropontin, Crystal Matrix Protein, renal Lithostathine. The role of these proteins is stressed.