Amyloidosis is a heterogeneous group of disorders characterized by extracellular deposition of abnormal protein fibrils, which are derived from different proteins. The Amyloid A Antibody reacts with native and fixed amyloid fibrils. The Antibody also reacts with amyloid deposits in many tissues including kidney and rectum. Cross-reactivity with serum precursor of protein AA has been observed. The application of Congo Red, Amyloid A and Amyloid P in tissues with amyloid deposits has been shown to be superior to Congo Red alone.