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.