In this study, a hypothesized adverse outcome pathway (AOP) linking inhibition of thyroid peroxidase (TPO) activity to impaired swim bladder inflation was investigated in experiments in which fathead minnows were exposed to the TPO inhibitor 2-mercaptobenzothiazole (MBT). Results show that anterior, but not posterior, swim bladder inflation was impacted by exposure to MBT supporting the development of an AOP linking a specific thyroid-disrupting molecular initiating event to a significant phenotypic outcome. Results also suggest an alternative short-term in vivo test with larval fathead minnows that could be used to screen chemicals for thyroid disrupting activity and possibly distinguish thyroid disrupting modes of action. The dataset contains information on TPO expression, thyroid hormone concentrations, and swim bladder inflation measurements in larval fathead minnows. This dataset is associated with the following publication: Nelson, K., A. Schroeder , G. Ankley , B. Blackwell, C. Blanksma, S. Degitz , K. Jensen , R. Johnson , M. Kahl , D. Knapen, P. Kosian , R. Milsk, E. Randolph, T. Saari, E. Stinckens, L. Vergauwen, and D. Villeneuve. Impaired anterior swim bladder inflation following exposure to the thyroid peroxidase inhibitor 2-Mercaptobenzothiazole Part I: Fathead minnow. AQUATIC TOXICOLOGY. Elsevier Science Ltd, New York, NY, USA, 173: 192-203, (2016).