The nephrogram is a radioactive curve traced from the renal area after 131I-o-iodomaluran (131I-ortho-I-hippuran, OIH for short) is injected into the vein, enters the kidney with the blood flow, is absorbed and secreted by the tubular epithelial cells and glomerular filtration into the tubular lumen of the kidney, is flushed to the renal pelvis by primary urine, and then excreted to the bladder with the urine flow. The height and speed of the rising curve mainly reflect the effective renal plasma flow and the function of renal tubular epithelial cells; the rate of the falling curve mainly reflects the amount of urine flow and the patency of the upper urinary tract, including the renal tubules. The nephrogram can be obtained from the left and right kidney areas respectively, and its clinical application is as follows: (1) to understand the total renal function (reflected by the larger value of the renal index on both sides); (2) to understand the fractional renal function; (3) whether there is any significant difference between the renal function (including blood supply status) on both sides; (4) to understand the fractional upper urinary tract patency; (5) to differentiate the upper abdominal mass from the kidney. There are no contraindications to this test, and it can be performed even in those who have a history of allergy to iodine oil contrast agent.