A 12-yr-old girl with the syndrome of hyperthyroidism due to inappropriate TSH secretion, who had no evidence of pituitary tumor, was studied in detail. She had undergone two thyroidectomies for recurrent goiter and hyperthyroidism before referral. Basal serum TSH levels were extremely high (maximum 173 μU/ml), and the TSH response to TRH was exaggerated (peak, 675 μU/ml)- The serum α-subunit of TSH was normal. PRL and other anterior pituitary hormone studies were normal. Dopamine infusion at 2 and 4 μg/kg min partially suppressed TSH and PRL secretion and their responses to TRH. Bromocriptine had a paradoxical effect, resulting in an increase in TRH-stimulated TSH levels. Pergolide, a newer dopamine agonist, significantly decreased per basal serum TSH and blunted the TSH response to TRH; however, despite progressive dose increases, her TSH level was not reduced to normal. © 1984 by The Endocrine Society.