Abstract.Octreotide usually induces long-acting inhibition of GH secretion without rebound hypersecretion. We report a patient with acromegaly who showed rebound elevation of GH and insulin-like growth factor-1(IGF-1) after octreotide withdrawal.The patient responded remarkably to octreotide therapy with normalization of GH and IGF-1 and shrinkage of pituitary macroadenoma.Octreotide therapy was stopped when he developed liver dysfunction.GH and IGF-1 were markedly elevated for two weeks after cessation of octreotide.Key words:Acromegaly, Octreotide, Rebound hypersecretion, Liver injury (Endocrine Journal 47: 635-638, 2000) OCTREOTIDE has been introduced as a useful therapeutic adjunct in the treatment of active acromegaly [1, 2]. It has been shown to induce long-acting inhibition of GH secretion without rebound hypersecretion [3, 4]. We report a case of GH rebound elevation after octreotide withdrawal due to liver injury in a patient with active acromegaly, since very few acromegalics are reported to exhibit rebound phenomena [5][6][7]. zyme inhibitor therapy was begun. He also had stress polycythemia due to heavy smoking. The patient had mild acromegalic features with diffuse goiter. Fasting serum GH and insulin-like growth factor-1 (IGF-1) were 4.7 pg/L and 550 ,ug/L, respectively. Serum PRL was normal (4.9 ,ug/L), as were thyroid function tests. Oral glucose loading partially suppressed GH levels (nadir; 1.5 ~€g/L). Serum GH levels were not altered by either TRH or GnRH. However, GHRH, insulin-induced hypoglycemia or dopamine infusion remarkably induced GH secretion (peak; 19.5 pg/L, 41,ug/L or 28.5 pg/L, respectively). Oral administration of bromocriptine (2.5 mg) evoked GH increase, whereas subcutaneous injection of octreotide (50 pg) effectively suppressed GH levels for up to 6 hours ( Fig. 1). Magnetic resonance imaging (MRI) of the brain showed macroadenoma of 20 mm diameter with suprasellar extension and possible invasion into the left cavernous sinus. He had been treated preoperatively with Octreotide in order to improve surgical outcome.Treatment with octreotide was started at a dose of 50 ig subcutaneously three times a day, but was increased to 100 ug three times daily one week later.