The preparation and use of radioiodinated Congo red in detecting amyloidosis.

Congo red concentrates in amyloid tissue. This study was undertaken to prepare a radioactive congo red which would concentrate in amyloid, permitting external counting and, thereby, scanning and localization, as well as blood concentration measurement. Two methods were used to trace-label the dye to an adequate specific activity for such studies. Injection into guinea pigs with amyloidosis resulting from induced chronic scurvy indicated deposits and radioactivity in the liver and other organs. The “tagged” dye shows promise for locating amyloid and may serve as a means for evaluating drugs for the resorption of amyloid. The method of direct radioiodination is applicable to other similar chemical compounds.