Thyroglobulins (Tgs) have been obtained from macro-microfollicular goiter, toxic adenomas, papillary carcinomas and metastatic lympho-node and chromatographed by gel filtration. The 19S Tgs so obtained have been characterized by isoelectric focusing (IEF) and immunoblotting. IEF showed microheterogeneity pattern of Tgs from normal tissue, macro-microfollicular goiter and toxic adenomas to be within pH range from 4.2 to 4.5, while that from papillary carcinomas and metastatic lympho-node showed a wider microheterogeneity. Passive blotting of focused Tgs and immunoreaction with rabbit anti-Tg peroxidase conjugated antibody have been carried out and a positive reaction for all examined samples have been evidenced. Also two bands, focused at more cathodic pH value (pH 4.7), observed in IEF patterns of Tgs from carcinomas and metastatic lympho-node, gave a positive reaction with anti-Tg conjugated antibody. These differences observed in IEF and immunoblotting patterns of Tgs from papillary carcinomas and metastatic lympho-node are discussed in this report.