Recent developments in molecular biology and the accessibility of techniques for clinical research have led to a better understanding of the background of common thyroid diseases. The cloning and sequencing of the thyroid stimulating hormone receptor, thyroid peroxidase and thyroglobulin, and the characterization of the protein-DNA interaction during thyroid hormone action, as well as the discovery of intracellular signal transduction pathways were the most important steps which resulted in new diagnostic and therapeutic approaches. New explanations of thyroid autoimmune processes are being investigated.