The concentrations of sodium, potassium, calcium, magnesium, phosphorus, sulfate, citrate and oxalate in the urine of normal subjects were compared to the concentrations in urine of calcium oxalate stone-forming patients. Because of the large volume excreted by stone-forming patients the urine contained less concentrations of sodium, potassium, magnesium, phosphorus, sulfate and citrate than did the urine from normal subjects. The urinary concentrations of calcium and oxalate were similar in the 2 groups and, thus, the calculated supersaturation of calcium oxalate was greater in the urine of stone-forming patients than in the urine of normal subjects. Orthophosphate therapy increased the urinary concentration of alkali ions and phosphate but reduced urinary calcium concentration, thereby causing a reduction in urine supersaturation with calcium oxalate. There was no discernible correlation between the phosphate-induced changes in urine supersaturation and the presence or absence of continued calculus formation.