Renal morphology and renal function were studied with iodine-123-hippurate in 98 patients with various renal diseases. Sequential scintigraphy with iodine-123-hippurate demonstrates much better renal blood flow, morphology and function than iodine-131-hippurate. A method of labeling hippurate in a short time (2 h) with high efficiency (95--100%) is described. Radiation exposure to various organs was calculated and significant differences in radiation exposure to the thyroid are demonstrated.