The main function of the thyroid gland is to make hormones, T4 and T3, which are essential for the regulation of metabolic processes throughout the body. Caveolae harbour is the key enzymes involved in this iodide organification. The analyses of thyroids from normal mice and caveolin-1 Knockout mice (mice deficient in caveolin) have been performed using the SIMS imaging. In the thyroid of control mice, the epithelium is homogeneous and iodine (I-127) is observed in the follicle lumen. In Knockout mice, we observe an accumulation of intracellular vesicles and apoptotic nuclei resulting from oxidative stress due to H2O2 overproduction also inducing apical lesions of the thyrocytes, at the site of iodine organification and H2O2 generation. We also observe in the Knockout mice an accumulation of I-127 in the cellular cytoplasm and an absence of the iodine in some follicular lumina, indicating a problem at the level of iodine organification. Crown Copyright (C) 2008 Published by Elsevier B. V. All rights reserved.