Fifty-four clinically euthyroid patients were evaluated 1 up to 17 yr after external irradiation to the neck for Hodgkin's disease. T4 level was decreased in 6%, while basal TSH level was increased in 44%, and TSH response to TRH was increased in 66% of the patients with normal basal TSH level. Thyroid iodine content (TIC), measured in 50 patients, was below 5 mg in 18. The 29 patients with normal basal TSH level had a mean TIC (6.8 +/- 2.7 mg) significantly lower (p less than 0.01) than the control population (14.6 +/- 5 mg). A significant positive correlation was found between log T4 and log TIC (r = 0.55, p less than 0.01). Thyroglobulin (Tg) level was increased in 53% of the patients with no palpable thyroid abnormality. It was not related to TSH level but was related to younger age at irradiation. T4 treatment decreased Tg level to the normal range in 5 of 8 patients. These facts suggest subclinical thyroid abnormalities and patients with elevated Tg levels should be considered at risk for developing a thyroid tumor.