Early pulmonary metastases may be difficult to detect roentgenographically because of their small size. The usefulness of routine, 131I, whole-body scintiscanning in the follow-up of patients with thyroid carcinoma has not been adequately stressed. The following case report demonstrates the value of whole-body radioiodine scintiscanning in detecting pulmonary metastases from thyroid carcinoma before they are visible on the chest roentgenogram. Only three other similar cases could be found in the English literature (1–3). The use of a whole-body counter for measuring total-body 131I retention in such patients is also briefly discussed. M.B., a 25-year-old housewife, underwent a total thyroidectomy and right neck dissection on July 30, 1964, for carcinoma of the thyroid. Seven of 17 nodes were positive for tumor. The histologic diagnosis was papillary variant of follicular adenocarcinoma. In November 1965 the patient was referred to the University of Missouri Medical Center after the referring physician removed a benign lymph node from her neck. On physical examination she was a well developed, healthy-appearing young woman with no evidence of tumor. An 131I whole-body scintiscan was suggested. L-Thyroxine medication was stopped for two weeks prior to administration of 800 μCi of 131I. Forty-eight hours later the scan was performed. It showed no activity in the neck or skeletal system, but diffuse uptake was unexpectedly demonstrated throughout both lungs (Fig. 1). The chest roentgenograms were reviewed by several radiologists, and all agreed they were completely normal (Fig. 2). L-Thyroxine was recommended. The patient returned in January 1966 for follow-up and was asymptomatic. The L-thyroxine was again discontinued for two weeks, and TSH, 10 units daily, was administered for three days. On the third day 1 μCi of 131I was given orally, and a whole-body retention study was performed at the low-level radiation laboratory. There was 1.9 per cent retention at ninety-six hours (Fig. 3), indicating functioning thyroid tissue. The 131I whole-body scintiscan again showed diffuse pulmonary uptake, but the roentgenogram remained normal. On Jan. 12, 1966, the patient was given 75 mCi of 131I orally as a therapeutic dose. She continued to feel well, and a repeat scintiscan in April 1966 showed no activity in the lungs (Fig. 4). A second whole-body retention study showed no evidence of functioning thyroid tissue (Fig. 3). The patient was last seen in February 1967 and was feeling well. No evidence of thyroid tissue was found on physical examination, chest roentgenogram, or scintiscan. Discussion In patients whose thyroid gland has been ablated, either surgically or by radiation, thyroid metastases usually take up radioactive iodine (4). When the scintiscan is positive these lesions are amenable to 131I therapy. The effectiveness of 131I therapy is illustrated by this case and is well documented (5). Technetium 99m has been used recently in the scanning of thyroid metastases and may be helpful in detection of nonfunctioning thyroid tissue (6). In the future, whole-body scanning with both 131I and 99mTc in combination may allow earlier diagnosis and treatment in a higher percentage of thyroid metastases.