This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Recombinant human (rh-TSH) is routinely used in the monitoring if patients with thyroid cancer. Its administration stimulates thyroid radioiodine uptake (RAIU) and thyroglobulin release without the need to withdraw thyroid hormone therapy and render the patient hypothyroid. In this matter, a rh-TSH is FDA approved for the management of thyroid cancer and its safety in various subgroups, including euthyroid subjects and in those with nodular goiters, has been established. In normal euthyroid subjects and in patients with non-toxic multinodular goiters recombinant human TSH increases the radioiodine uptake (RAIU) at 24 hours. However, the precise duration of this increase in the RAIU from rh-TSH has not yet been described. The purpose of our study is to examine the effect of rh-TSH on the RAIU at 24, 48, and 72 hours after its administration. In addition, we will examine the duration and peak effect where the greatest increase on the RAIU is seen. Ultimately, this may facilitate post-operative management of thyroid cancer, as it will provide us with an optimal time frame at which to measure RAIU for improved visualization of thyroid metastases and residual thyroid bed tissue. We plan to recruit 15 subjects with normal thyroid glands and normal thyroid function. We will administer 0.1 mg of rh-TSH to all subjects and measure the 24-hour RAIU following the administration of 123-I at 24, 48, and 72 hours after rh-TSH administration. This information will also provide guidance for the optimal time after rh-TSH administration to give 131-I for the ablation if residual thyroid tissue after thyroidectomy for thyroid cancer and to decrease the size of large nodular non-toxic goiters.