Recognizes a glycoprotein of 330kDa, identified as thyroglobulin. Antibody to thyroglobulin has been shown to be useful in positive identification of thyroid carcinomas of the papillary and follicular types. and stains thyroglobulin in follicular epithelial cells as well as colloid tissue. Demonstration of thyroglobulin in a metastatic lesion establishes the thyroid origin of the tumor. Adenocarcinomas of non-thyroidal origin are not reactive.