['Crystal growth and aggregation are the important mechanisms of calcium oxalate stone formation in the kidney. Recently we successfully purified trefoil factor 1 from human urine and used an oxalate depletion assay to indirectly infer its inhibitory activity against calcium oxalate crystal growth. We searched for direct evidence to define the inhibitory activity of urinary trefoil factor 1 against calcium oxalate crystal growth. Moreover, we also evaluated whether urinary trefoil factor 1 has any effects on calcium oxalate crystal aggregation and transformation.', 'Isolated and aggregated forms of calcium oxalate monohydrate crystals were produced in the absence or presence of 7, 70 and 700 ng/ml urinary trefoil factor 1, nephrocalcin as a positive control or lysozyme (Sigma-Aldrich) as a negative control.', 'The data clearly indicated that urinary trefoil factor 1 and nephrocalcin at physiological levels could effectively inhibit calcium oxalate monohydrate crystal growth and aggregation, whereas lysozyme did not affect the growth and aggregation of calcium oxalate monohydrate crystals. At a supraphysiological concentration of 4 microg/ml urinary trefoil factor 1 and nephrocalcin could transform calcium oxalate monohydrate crystals to the dihydrate type, which has much less adsorptive capability.'] Is urinary trefoil factor 1 a novel potent inhibitor of calcium oxalate crystal growth and aggregation?