This article discusses the automation of thyroid function testing. The needs for automation are included in the introduction. The issues concerning automation of immunoassay are discussed, including homogeneous or heterogeneous immunoassay, competitive or immunometric assay, reagent stability, data management, sample management, signal detection, and the disadvantages of automation. Individual immunoassay systems are summarized with a table outlining the key features. Both technical and clinical performance of automated thyroid function testing are described. The article ends with a discussion of the future trends of automated immunoassay testing.