All adult patients with differentiated non-medullary thyroid cancer who are preparing for ablation therapy are eligible for participation. Patients will be randomized to one of two different dosing regimens of Thyrogen® (Registered Trademark). Participants will undergo two 131I whole body scans: one after Thyrogen® (Registered Trademark) while taking thyroid hormone suppressive therapy and the second after withdrawal from thyroid hormone. 131I ablative therapy will be given under hypothyroid conditions at the completion of the dosimetry study.