Thyroglobulin antibody cocktail has been shown to react with human thyroglobulin, staining thyroglobulin in follicular epithelial cells as well as colloid tissue. Clones 2H11+ 6E1 have been shown to be useful in positive identification of both papillary and follicular types of thyroid carcinomas. Demonstration of thyroglobulin staining via immunohistochemistry in a metastatic lesion establishes the thyroid origin of the tumor. Poorly differentiated carcinomas of the thyroid are frequently thyroglobulin negative. Adenocarcinomas from a non-thyroid origin are not reactive.