We measured serum thyroglobulin (Tg), a marker of thyroid cancer metastases, in patients operated on with total thyroidectomy for thyroid carcinoma on three different occasions at the beginning of follow-up: 30 days before radioactive iodine therapy (RAI) for remnant ablation (and at least 40 days after thyroidectomy in euthyroidism), at the time of RAI (in hypothyroidism), and 7 days after RAI in euthyroidism. The gene discussed is TG; the disease is thyroid cancer.