Determination of the sequence of the human genome has led to a large expansion of research in this area. Several studies on single nucleotide polymorphisms, i.e. variations in the genome that occur in > 1% of the population, have been published in recent years. In the thyroid field, information about variation in relevant genes is also forthcoming, which is not surprising as these polymorphisms are thought to play a role in determining each individual's thyroid hormone set-point. So far, research has focused mainly on genetic variation in the thyroid-stimulation hormone receptor and the deiodinases, and their association with thyroid parameters and/or clinical endpoints, such as insulin resistance. However, with the characterization of specific thyroid hormone transporters, a new field of research is emerging.