The problem of assessing the degree of parenchymal injury following renal trauma has caused a great deal of difficulty and controversy in the past several years. In the majority of cases, plain abdominal roentgenograms as well as intravenous urograms prove inadequate (2, 7), and the fact that only a small percentage of these patients undergo laparotomy further compounds the difficulty in clinical evaluation. In the past three years, direct visualization of the intrarenal vasculature with aortography and selective renal angiography has contributed greatly to the better understanding of the nature of renal injuries (7), but renal angiography may not be necessary in all cases of renal trauma. In attempts to understand further the nature of these injuries and to find a simple and fully innocuous method of studying kidney trauma, the mercury-197 chlormerodrin renal scan was utilized. The simplicity of the procedure makes it easily adaptable for use in smaller centers where angiographic technics may not be readily available. It is free from complications, and there are none of the allergic problems that may exist with organic iodides. The purpose of this communication is to demonstrate the value and discuss the place of scanning as an addition to the presently accepted methods of evaluating the extent of injury in renal trauma. Material and Method Twenty-eight patients (22 males and 6 females) with an age range of seven to eighty-four years and an average age of twenty-six were subjected to scanning. In a twenty-ninth, arteriovenous fistula of the kidney followed renal biopsy, but the scan was technically unsatisfactory and therefore this case will be omitted from the statistical analysis. The study was undertaken in conjunction with an investigation of renal angiography in renal injury; the results of this latter study will be published separately. In 24 patients the injury was acute; all of these gave a history of flank or abdominal trauma associated with gross or microscopic hematuria. These patients were studied from several hours to two weeks after injury. In 4 cases the renal trauma was old. Costovertebral tenderness was present in 24 of the 28 (86 per cent). The conventional renal scan (5) was performed with 1.5 mCi Hg197 chlormerodrin per kilogram of body weight. Hg197 was used instead of Hg203 to reduce kidney radiation exposure (13, 14). The Picker Magnascanner equipped with a 3 × 2-in. sodium iodide (thallium-activated) crystal and a 19-hole focusing collimator was employed. An isotopic window of 0.050–0.095 MeV was used for the peak gamma energy of 0.079 MeV of Hg197. The scan speed was 36 cm per minute, and the line spacing was 0.5 cm. The scan was obtained with the patient in the prone position one hour after the intravenous injection of the radio- nuclide.