SUMMARY: 1. A study has been made of the compounds synthesized by and present in the thyroid gland of larval and adult Xenopus laevis using radioactive iodine and chromatography. 2. Tadpoles undergoing active metamorphosis produced thyroxine and trace amounts of 3:5:3′-triiodothyronine. Less thyroxine and no triiodothyronine was detected in tadpoles approaching the end of metamorphosis, and neither compound was detected in tadpoles in early stages of metamorphosis. Adult toads produced thyroxine and trace amounts of triiodothyronine. The presence of monoiodotyrosine and diiodotyrosine was a constant finding. 3. It is suggested that the synthesis of thyroid hormones in amphibia is similar to that in other vertebrates.