Purpose: Temporary tracheal occlusion induces lung growth in congenital diaphragmatic hernia (CDH) but has significant drawbacks because the device must be removed in utero. We devised a gel plug (GP) that can be placed in the fetal trachea in a rabbit model of CDH to provide temporary tracheal occlusion and evaluated its effect on lung growth and postnatal ventilation mechanics. Methods: In each of 16 pregnant rabbits, experimental CDH was created in 4 fetuses. These were randomized to intratracheal instillation of a fibrin GP, tracheal suture ligation, intratracheal instillation of normal saline, or sham amniotomy. Unmanipulated fetuses of the litter without CDH served as controls. Fetuses were harvested at gestational day 29 and mechanically ventilated to determine lung compliance and airway resistance. Fetal lung-to-body weight was compared among the groups. Results: Mean fetal lung-to-body weight was higher in GP-treated fetuses than in the normal saline group, although not as high as that in fetuses subjected to tracheal ligation. Gel plug-treated fetuses had the highest airway resistance, whereas non-CDH control fetuses had the most compliant lungs. Conclusions: Prenatal instillation of an intratracheal GP leads to increased postnatal lung mass in rabbit fetuses with CDH but also increases airway resistance. © 2012 Elsevier Inc. All rights reserved.