Laboratory examinations are an essential part of the diagnostic investigation of thyroid diseases. They range from assays of the thyroid hormones and thyroid-stimulating hormone, through antibody investigations, to tumour markers. Over the past years there have been various innovations that are relevant to the investigation of thyroid diseases and that have therapeutic implications. They include, in particular, antibody investigations, including the determination of TSH-receptor antibodies but also the introduction of highly sensitive thyroglobulin assays. This book summarises established and new developments in the laboratory investigation of thyroid diseases and is a useful guide to clinical practice with material that is right up-to-date.