The 24-hour urinary excretion of citrate was measured in 83 normal persons and in 132 consecutive patients with idiopathic calcium urolithiasis, uninfected urine, and normal renal function. The urinary excretion of citrate in normal men was not significantly different from that in normal women (P greater than 0.05). There was a significant (P less than 0.001) increase of urinary citrate excretion with increasing age in normal persons. No increase of urinary citrate excretion with age was demonstrated in stone formers. There was no statistically significant difference between active and inactive stone formers in regard to regression of the citrate/calcium ratio or the citrate/uric acid ratio, and there was no difference in these ratios between men and women considered separately or in subgroups by hypercalciuria or hyperuricuria or by individual age. Hypocitraturia was found in 29.2% of patients with idiopathic calcium urolithiasis. No relationship could be demonstrated between the 24-hour urinary excretion of citrate and severity of stone disease before presentation at our clinic or the frequency of stone growth or new stone formation at follow-up. Twenty-two of 35 patients with hypocitraturia had multiple urinary citrate measurements. In 15 of these 22 patients, at least one normal urinary citrate measurement was obtained. Further prospective study is required to establish the value of urinary citrate determinations in patients consuming an uncontrolled diet in an outpatient setting.