Thyrotropin-releasing hormone (TRH) was administered iv to 8 patients with renal failure, 8 normal men, and 5 children. Injection of 1600 μg TRH as a bolus to healthy adults or a smaller dose to children resulted in a normal pattern of TSH release. The prolonged release of TSH which occurred after stat injection of 400 μg TRH to the patients with greatly diminished renal function was similar to that found after a 4-hr infusion of 1600 μg in normal men. In the men receiving the iv infusion, TSH levels began to diminish after 2 hr, despite the continued infusion of TRH for an additional 2 hr. An unexpected increase of hGH was also found in 7 of 8 patients with renal failure after injection of TRH.