of Renal CZemance

metabolism of radioiodine, we have used the equational relationships developed, to calculate quantities related to renal function. The general principles em-ployed have been used by others for chemically analyzed substances uti-lized in clinical tests (1-3). We have made specific use of the observations ob-tainable with radioactive iodine, in conditions where not all of the substance was being excreted in the urine (unusual for clearance calculations), have ad-vanced a method for using the curve of urine content as well as the curve of blood concentration, and have compared the results obtained by using these methods with a more usual method for estimating clearance. DIRECT CALCULATION OF CLEARANCE The methods used for determination of amounts of radioactive iodine in the blood and urine have been previously described (4). Clearance, calculated directly, is obtained by observing the rate of excretion into the urine during a period of time, and dividing this quantity by the blood concentration during that period