The composition of 24 h urine samples collected by 50 normal controls and 76 stone formers (30 hypercalciurics, 13 hyperuricosurics and 33 patients without metabolic abnormalities) were studied. Statistically significant multiple regression equations were obtained between calciuria and the urinary excretions of sulfate, citrate, sodium and creatinine. The three former ions were selected as variables because they were assumed to affect the tubular fluid concentration of ionized calcium and interfere with the reabsorption of calcium. Urinary creatinine was included because it increased the statistical significance of the multiple regression equations; it is assumed to be a function of body size. The regression equations differed between both groups of subjects because stone formers excreted significantly more sulfate and less citrate than controls. The four factors considered (sulfate, citrate, sodium and creatinine) account for 28.3, 6.8, 7.3 and 26.4% of the total variation of calciuria of normal controls and 45.0, 2.6, 8.6 and 14.7%, respectively, for stone formers.