The various causes of persisting hyperthyroxinemia without hyperthyroidism are discussed after short case histories of an infant with hyperthyroxinemia due to TBG excess, discovered by newborn screening for congenital hypothyroidism and a girl with peripheral resistance to thyroid hormones disclosed by investigation of a small goiter. The differentiation of these various causes by thyroid function-tests is indicated. Though the anomalies leading to euthyroid hyperthyroxinemia are usually harmless their timely recognition, also in other members of the family, will prevent erroneous diagnosis and treatment of hyperthyroidism.