1. Variations with age in body weight, urine volume and calcium and creatinine excretion were determined in 246 normal subjects and 305 patients with calcium-containing renal stones.

2. Body weight, urine volume and creatinine excretion increased with age to a maximum in the third decade in both male and female controls and stone-formers. Thereafter body weight and urine volume did not change appreciably but creatinine excretion decreased.

3. In normal subjects the daily excretion of calcium and calcium concentration increased in the first two decades and remained relatively constant thereafter until the eighth decade when they decreased. The calcium/creatinine ratio was high in the first decade and fell during the second and third decades. Thereafter it remained relatively constant in men until the eighth decade when it fell. In women, however, there was a second rise in the fifth and sixth decades. The calcium/body weight ratio remained relatively constant with age until the eighth decade, when it fell.

4. Patients with renal calculus showed similar variations in calcium excretion with age. The mean values, however they were expressed, were higher than those in normal subjects of the same age and sex.

5. The daily excretion of calcium was higher in men than women, whether normal subjects or stone-formers. This difference was abolished when calcium excretion was related to body weight and reversed when excretion was related to creatinine.

6. Comparison of the present data with previous data from the same population indicated that the mean daily excretion of calcium by both normal subjects and patients with renal calculi has increased during the last decade.

7. The significance of these observations in relation to calcium homeostasis and renal calculus formation is discussed.

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