Abstract: Radiolabeled angiotensin converting enzyme inhibitors having the general formula: ##STR1## wherein X is a radiolabeling substituent, preferably a radiolabeling halogen substituent such as .sup.123 I, .sup.125 I, .sup.131 I, .sup.75 Br or .sup.77 Br,Y is hydroxy, alkoxy containing from 1 to 6 carbon atoms, phenoxy, benzyloxy, or amino,R.sub.1 is hydrogen or methyl,R.sub.2 is hydrogen, an ester moiety hydrolyzable under mammalian in vivo conditions, such as alkyl of 1 or 2 carbon atoms, phenyl or benzyl, or an ionically bonded anion of a physiologically acceptable non-toxic salt, andm is an integer of from 1 to 6, are useful as in vivo radioimaging compounds for mammalian sites.