Abstract: Anionic azo compounds which, in the free acid form, have the Formula (1): ##STR1## wherein: Ar and Ar.sup.1 are each independently aryl or substituted aryl providing at least one of Ar and Ar.sup.1 has at least one substituent selected from COOH and COSH;J and J.sup.1 are each independently of formula (2), (3) or (4): ##STR2## each R.sup.5 is independently selected from H, alkyl, substituted alkyl, alkoxy, halogen, CN, ureido and NHCOR.sup.6 ;R.sup.6 is H, alkyl, substituted alkyl, aryl, substituted aryl, aralkyl or substituted aralkyl;each T is independently alkyl;each W is independently selected from H, CN, CONR.sup.10 R.sup.11, pyridinium and COOH;each m is an alkylene chain having 2 to 8 carbon atoms;B is H, alkyl or COOH;R.sup.1, R.sup.2, R.sup.3, R.sup.4, R.sup.10 and R.sup.11 are each independently H, alkyl or substituted alkyl;L is a divalent organic linking group;n is 0 or 1;each X is independently carbonyl or a group of the Formula (5), (6) or (7): ##STR3## Z is OR.sup.7, SR.sup.7 or NR.sup.8 R.sup.

Abstract: The presence and location of amyloid deposits in an organ or body area of a patient is effected by intravenous administration of novel radioactive iodine-labeled amyloid binding compounds and preferably .sup.123 I-labeled compounds to the patient and sensing radiation emitted from the organ or body area. Novel non-radioactive iodine substituted amyloid binding compounds and amyloid binding compounds which are readily iodinated are further aspects of the invention.