A 53-year-old woman with an early form of de Quervain's disease involving both thyroid lobes was found to have her thyroid uptake of iodine suppressed, although the serum thyroid hormone concentrations were normal while the administration of TRH resulted in significant increase in the serum TSH concentrations. After administration of TSH the thyroid reserve was found to below. The diagnosis of sub-acute thyroiditis was confirmed on biopsy. The above data seem to indicate that the suppression of the thyroid uptake in the early stage of de Quervain's disease may be directly caused by the inflammatory condition of the gland, rather than, as is usually the case, by the excess of thyroid hormones and, consequently, by the suppression of pituitary TSH secretion.