By applying cutting-edge technologies at the very forefront of endocrine-disruption research, this XENROID project will investigate environmental xenobiotics that pose a threat to three highly sensitive vertebrate indicator species; African clawed frog (Xenopus laevis), California sea lion (Zalophus californianus) and polar bear (Ursus maritimus). Thyroid and steroid hormone systems are most often studied independently, but it is imperative to investigate the two in union, and that is the strength and focus of this study.The applicant will collaborate with 3 high-ranked research laboratories at University of California Berkeley (outgoing host), , US Marine Mammal Center, and University of Copenhagen (reintegration host).Of special note, this proposal is a revision of proposal no. 302194 from FP7-PEOPLE-2011-IOF, which scored 85.90%. The current proposal includes increased focus on the training of the applicant and on the development of new scientific tools. To enhance research collaborations and increase knowledge facilitation, the revised proposal includes three institutions within the Bay Area of California (new collaborators include high-caliber scientific laboratories at Berkeley and the Marine Mammal Center), while excluding work at the National University of Singapore and the US Environmental Protection Agency listed in the previous submission.Consequently, the ‘environmental chemistry and environment fate of thyroid hormones’ component of the previous proposal has been removed, and the project now includes a comprehensive and focused investigation of endocrine health and effects of the selected wildlife species.