My laboratory investigates the iodide-concentrating protein transport system, known as NIS, and its key role in pulling iodide from the bloodstream and into cells of the thyroid gland, salivary glands, and lactating mammary glands. Our research has ramifications in thyroid disease and breast cancer. Iodide is scarce in the environment and is an essential component of the thyroid hormones triiodothyronine (T3) and thyroxine (T4). These hormones play crucial roles in regulating metabolism in virtually all tissues and in governing the growth and maturation of the nervous system, skeletal muscle, and lungs of the developing fetus and newborn. NIS-mediated iodide uptake in the thyroid gland is the extremely important first step in synthesizing T3 and T4.More recently, we have identified spontaneous NIS mutations as the cause of congenital iodide transport defect (ITD) in patients and we have characterized these mutations, leading to important structure/function insights regarding NIS. We also found that endogenous NIS expression occurs in breast cancer -the basis for our suggestion that radioiodide may be a novel approach for the diagnosis and treatment of this disease. In the area of public health, we have found that perchlorate, a pollutant found in water supplies in 22 states, poses a greater health risk than previously realized, particularly to nursing infants. Our research showed that NIS translocates perchlorate from the mother’s bloodstream and into breast cells, where it becomes concentrated in breast milk. In fact, NIS exhibits a higher affinity for perchlorate than for iodide. Nursing mothers exposed to high levels of perchlorate in drinking water may, therefore, provide insufficient iodide to their babies, compromising their babies’ ability to synthesize sufficient amounts of T3 and T4 hormones and potentially causing them to become mentally impaired.