A severely malnourished 87-yr-old man presented with hypoglycemia. Serum GH levels were elevated, and serum levels of insulin-like growth factor I (IGF-I), IGF-binding protein-3, and GH-binding protein were extremely reduced. The patient's GH was biologically active. Administration of GH for 4 consecutive days resulted in a slight increment in serum IGF-I levels, but no elevation of serum IGF-binding protein-3. The expression of GH receptor messenger ribonucleic acid in the liver was greatly reduced. An autopsy revealed a Rathke's cleft cyst confined to the sella turcica. Immunohistochemical studies for GH showed that there was nothing to suggest a tumor overproducing GH. In addition, TSH levels were elevated in the presence of normal thyroid hormone levels, and there was a cluster of cells showing strong immunohistochemical staining for the TSH beta-subunit in the pituitary. In this patient, the decreased expression of GH receptor messenger ribonucleic acid in the liver may have been responsible for the GH resistance, which was probably caused by malnutrition.