The goal of this proposal is to produce and test high specific activity Ultratrace iobenguane I 123 in normal human volunteers. The low specific activity iobenguane I 123 has been shown to be useful for the detection and staging of neuroendocrine tumors in adults and children and imaging neuronal activity in the heart. The innovation in this proposal is through the use of patented solid phase technology to produce a proven diagnostic agent at extremely high specific activity to increase sensitivity and specificity and lower radiation exposure to normal organs without the pharmacologically active cold carrier compound. The FDA considers iobenguane labeled with two different isotopes of iodine [I-131 and I-123] as two distinct drugs requiring distinct regulatory applications.