1. Diurnal variations in urine calcium oxalate and calcium phosphate activity products were observed in normal men and patients with recurrent calcium oxalate or mixed oxalate—phosphate renal stones.
2. Maximum and minimum calcium oxalate products were higher in the patients than in the controls, the difference being most marked in the patients with calcium oxalate stones.
3. Maximum and minimum calcium phosphate products expressed as octocalcium phosphate [(Ca8H2(PO4)6], brushite or hydroxyapatite, were significantly higher than normal in the patients with mixed stones but not in the patients with calcium oxalate stones.
4. The raised calcium oxalate products in the patients were due mainly to increased concentrations of Ca2+ ions; these, in turn, were due mainly to an increased rate of excretion of calcium. Raised calcium phosphate products were due mainly to hypercalciuria, combined with abnormally high urine pH values.
5. Patients with recurrent calcium stones appear to fall into two types: (1) patients with calcium oxalate stones associated with hypercalciuria, a normal or raised urine oxalate and a normal urine pH; (2) patients with mixed oxalate—phosphate stones associated with hypercalciuria, a normal or raised urine oxalate and a raised urine pH.
6. The implications of these findings in regard to treatment are discussed.