Obstructing the fetal trachea is a potent stimulus for fetal lung growth, but little is known about the factors that regulate this process. Our aim was to determine the role of growth hormone (GH) in regulating the increase in lung growth induced by obstruction of the trachea in fetal sheep. Twenty chronically catheterized fetal sheep, nine of which were hypophysectomized, were divided into four experimental groups: 1) control group (n = 4), 2) a group in which the fetal trachea was obstructed for 3 days (3-day obstructed; n = 6), 3) a 3-day obstructed group in which the pituitary was removed [hypophysectomized (HX)] and the fetus was given maintenance infusions of ACTH, thyroxine, and human GH (hGH; HX hGH 3-day obstructed; n = 5), and 4) a HX 3-day obstructed group in which the fetus was given maintenance infusions of ACTH and thyroxine (n = 5). Tracheal obstruction significantly increased fetal lung liquid volumes from 37.2 ± 3.2 ml/kg in control fetuses to 75.6 ± 9.0 ml/kg in 3-day obstructed fetuses, and the presence or absence of GH did not affect this increase. Similarly, the presence or absence of GH did not affect the increase in lung weight or protein content induced by 3 days of tracheal obstruction. However, in the absence of GH, 3 days of tracheal obstruction failed to increase total lung DNA content above unobstructed control values (107.9 ± 5.3 and 94.1 ± 7.0 mg/kg for control and HX 3-day obstructed groups, respectively). In contrast, 3 days of tracheal obstruction increased total lung DNA content to a similar extent in fetuses with an intact pituitary and HX fetuses that received GH replacement (126.0 ± 4.4 and 126.7 ± 4.0 mg/kg for 3-day obstructed and HX hGH 3-day obstructed groups, respectively). These data indicate that the absence of GH either abolishes or delays the acceleration in cell division caused by an increase in fetal lung expansion.