A 44-year-old man subjected to Hardy's operation for a treatment of acromegaly developed hyperthyroidism right after surgery. He had a normal thyroid function with a slightly suppressed TSH response to TRH before operation. Sudden onset of hyperthyroidism after surgery and suppressed TSH were compatible with Graves' disease. Hyperthyroidism was effectively treated with propylthiouracil (PTU) with slightly increased basal TSH level and normal response of TSH to TRH. Plasma GH level also increased after he attained euthyroidism, but inappropriate GH response to TRH persisted. It is suggested that increased endogenous TRH stimulated both TSH and GH release, but inappropriate GH response to TRH occurred irrespective of endogenous hypothalamic TRH. Bromocriptine, 5.0 mg/day, suppressed plasma GH level to a normal range with a concomitant suppression of PRL and TSH, both basal levels and responses to TRH.