Thyroid function in a patient during the course of de Quervain’s (subacute) thyroiditis. During the thyrotoxic phase (days 10 to 20), the serum TG concentration was greatly elevated, the FTI was high, TSH was suppressed; the erythrocyte sedimentation rate was 86 mm/hr, and the thyroidal RAIU was 2 percent. The thyroglobulin level and FTI declined in parallel. During the phase of hypothyroidism (days 30 to 63), when the FTI was below normal, a modest transient increase in the serum thyroglobulin level occurred in parallel with the increase in serum TSH. All parameters of thyroid function were normal by day 150, 5 months after the onset of symptoms.