This nuclear receptor assay system utilizes proprietary human cells engineered to provide constitutive, high-level expression of the human thyroid hormone receptor alpha (NR1A1), a ligand-dependent transcription factor commonly referred to as TRα. The reporter cells include the luciferase reporter gene functionally linked to a TRα-responsive promoter. Thus, quantifying changes in luciferase expression in the treated reporter cells provides a sensitive surrogate measure of the changes in TRα activity. The principal application of this reporter assay system is in the screening of test samples to quantify any functional activity, either agonist or antagonist, that they may exert against human TRα. TRα reporter cells are prepared using the proprietary CryoMite process. This cryo-preservation method yields exceptional cell viability post-thaw, and provides the convenience of immediately dispensing healthy, division-competent reporter cells into assay plates. There is no need for cumbersome intermediate treatment steps such as spin-and-rinse of cells, viability determinations, cell titer adjustments, or the pre-incubation of reporter cells prior to assay setup. The nuclear receptor reporter assays are all-inclusive cell-based assay systems. In addition to TRα reporter cells, this kit provides two optimized media for use during cell culture and in diluting the user"s test samples, a reference agonist, luciferase detection reagent, and a cell culture-ready assay plate.