The lack of suitable radiolabeled agents for photoscanning adrenal medullary tumors prompted synthesis of 4-hydroxy-3-iodo-(2), 3-hydroxy-6-iodo-(3), and 3-hydroxy- 54odophenylethylamine (4) radiolabeled with iodine-125. Radioiodination by isotope exchange was unsuccessful for 3 and 4, but the former was obtained by the direct radioiodination of rn-tyramine hydrochloride. Tissue distribution studies in dogs with 2 and ...