Conscious mature and immature rats were administered either saline or an ethanol (ETOH)-saline solution via a permanent intragastric cannula, and plasma growth hormone (GH) levels were measured by radioimmunoassay of external jugular blood samples drawn every 10 min through an indwelling Silastic catheter. Control injections of saline into the gastric cannula did not modify plasma GH concentrations, whereas both groups of rats which were administered ETOH showed significant decreases in plasma GH concentrations and no evidence of the pulsatile secretion of the hormone. Comparable increases in the area under the GH curve occurred following a challenge dose of GH-releasing factor in both saline- and ETOH-injected rats, indicating that pituitary responsiveness was the same for both groups. These results indicate that ETOH is capable of altering GH secretion in adult as well as prepubertal animals, via an action at the hypothalamic level.