Finlayson (1) has emphasized that merely measuring the 24-h excretion rates of different urinary constituents will be of little value in the study of patients with kidney stones or in determining the effectiveness of different therapeutic regimens, since the formation of kidney stones depends mainly on the concentration of urinary salts. This fundamental point has not been sufficiently emphasized in most papers on renal stones. Comparisons of patients with kidney stones and normal control subjects based on 24-h urine excretion rates are also unreliable because the excretion rates of some constituents are dependent on the rate of urine flow (24-h