A. Specificity for TR activity increases with technical difficulty and cost of the assays. B. One-week post-fertilization (PF) tadpoles are treated for 2–5 days, depending upon the assay, before assessing outcomes. TRE-luc: thyroid hormone response element driven luciferase reporter construct. NF-48: Nieuwkoop-Faber X. laevis developmental stage 48. C. Compounds used in this study: T3, 3,3’,5-triiodol-thyronine; T4, thyroxine; BDE-47, tetrabrominated diphenyl ether 47; TBBPA, tetrabromobisphenol A; TBT-Cl, tributyltin chloride; NH-3, synthetic TR antagonist.