Pyrophosphate does not influence calcium oxalate or calcium phosphate crystal formation in concentrated whole human urine.

1) Low pyrophosphate urine was generated by passage through a nylon coil bearing immobilised inorganic pyrophosphatase. High pyrophosphate urine was made by addition of inorganic pyrophosphate. 2) Urine samples of low, normal, and high pyrophosphate content were rapidly evaporated at 37 degrees C to 1,050 or 1,250 mosmol/L and the crystals formed studied by microscope, isotope and chemical methods. 3) Urinary pyrophosphate level had no significant effect upon calcium oxalate crystals formed in whole urine at pH 5.3 or 6.1, or calcium phosphate crystals formed at pH 6.8.