Comparison of Sirius red and Congo red as stains for amyloid in animal tissues.

Sirius red and Congo red were compared for specificity and sensitivity of amyloid staining in animal and human material. Previously described advantages of Sirius red as an amyloid dye were confirmed, as well as its disadvantage of lack of ultraviolet fluorescence. Two further disadvantages of Sirius red were discovered, both relating to animal material: (a) its unexpectedly weak staining of early experimentally induced amyloid deposits and (b) frequent uncontrollable nonspecific staining of fibrous tissues. It is therefore concluded that, overall, Congo red used by the improved alkaline technique of Puchtler, Sweat and Levine (1962) remains the best single method for demonstration of amyloid in both human and animal tissues.