Abstract This paper examines whether an antibody to serum amyloid A (SAA) protein is incorporated into amyloid deposits in vivo in murine reactive amyloidosis. First, monoclonal anti-SAA antibody was injected into amyloid-laden mice, and localization of the antibody was immunohistochemically assessed. Following the injection, plasma clearance of the antibody was analyzed. The antibody was detected in the amyloid deposits in spleen, liver, and kidney from mice killed on days 0-3 postinjection. The injected antibody disappeared more rapidly from the circulation of amyloidotic animals than from nonamyloidotic animals. The anti-SAA antibody can associate with amyloid deposits in vivo. Further applications, particularly amyloid imaging, should be investigated.