The therapist sees that the kidneys are shielded to prevent radiation nephritis when cancerocidal doses of irradiation are given for widespread abdominal malignant tumors (2, 4, 6, 7). Unavoidably, he may spare areas of tumor infiltrating or surrounding the kidney. It has recently been shown that, by causing temporary renal hypoxia, it is feasible to protect the normal canine kidney from large single doses of radiation. Before and during kidney irradiation vasoconstrictive doses of epinephrine were delivered selectively into the canine renal artery through a percutaneously placed catheter. Modifications of the infusion technic for clinical application were also described in this report (8). Preliminary results of the clinical application of this method of renal radioprotection to six patients were subsequently reported, along with a review of the experimental data (5). Materials and Methods Since November 1967, five courses of intensive abdominal irradiation and concomitant renal artery epinephrine infusions have been given to four selected patients with inoperable abdominal malignant tumors at the UCLA Clinical Research Center. Preliminary studies in each patient included a complete blood count, urinalysis, blood urea nitrogen, serum creatinine, creatinine clearance, liver battery, chest x-ray and bone survey, intravenous urography, Hippuran renogram, and Hippuran renal camera images.2 At time of placement of a percutaneous catheter in one renal artery, appropriate abdominal angiograms were also obtained to define the tumor more accurately and to visualize the kidney vasculature. Initially all patients had catheter placement into a renal artery by percutaneous axillary artery puncture. This route allowed a moderate amount of mobility, although the patients were confined mostly to bed or a bedside chair while the catheter was in place. A precurved #6 French Teflon catheter (radiopaque) was used, with no side-holes. The most efficient method of maintaining catheter position in the renal artery was to suture the catheter to the skin at the site of puncture. The indwelling catheter remained in place from twelve to twenty-three days. Periodic checks of catheter position were made by portal films and by fluoroscopy, at which time small amounts of Renografin-60 were hand-injected into the catheter. A bedside Sigmamotor pump or a tenfoot gravity drip delivering heparinized normal saline (1,000 /μ/liter) at the rate of one milliliter per minute kept the renal artery catheter open around the clock. One patient temporarily wore a battery-powered, portable pump which permitted him unrestricted mobility on the ward. In one instance (CASE III, below) the axillary artery approach was unsuccessful. A massive retroperitoneal tumor distorted the abdominal aorta, and the catheter tip would not remain within the left renal artery.