Epiglottic augmentation was evaluated in 7 horses, using 7 ml of polytetrafluoroethylene (polytef) paste injected submucosally on the ventral surface of the epiglottis. In 6 horses, an Arnold-Bruning intracordal injection syringe, specifically designed to inject polytef into paralyzed vocal folds in human beings, was used. At necropsy 60 days after surgery, group mean thickness measurement 20 mm from the epiglottic tip was 40% greater (P < 0.01) and, at the epiglottic attachment of the aryepiglottic fold, was 29% greater (P < 0.01) in the 6 polytef-augmented horses than in clinically normal nonsurgically treated controls. At necropsy, extensive epiglottic thickening was seen. This thickening was exclusively attributable to distention of submucosal areas in the ventral aspect of the epiglottis, with foreign body granulomata surrounded by fibrous connective tissue. In 1 horse, polytef paste was injected by use of a disposable syringe and needle. Excess ventral epiglottic swelling and exposed epiglottic cartilage was seen during subsequent endoscopy. At necropsy 60 days after surgery, the epiglottic contour remained deformed and a large deep mucosal ulcer was observed at the injection site. Histologic examination revealed necrotizing suppurative inflammation that extended into the epiglottic cartilage. Surgery was not technically difficult to perform through a laryngotomy, and all horses tolerated the procedure without apparent discomfort. Endoscopy performed after surgery revealed unremarkable and uniform response to the polytef paste in 4 horses, and in 3 horses, revealed excess swelling and inflammation of the ventral epiglottic tissue that resolved over time. Overdistention of the submucosal space with polytef may have accounted for the undesirable tissue responses that developed, including excess inflammation in the ventral epiglottic tissue in 3 horses, migration of polytef in 4 horses, and ventral mucosal ulceration in 3 horses. Thickening of the ventral epiglottic surface that was readily apparent in all horses at necropsy could not be reliably distinguished endoscopically in conscious horses. Qualitative changes in epiglottic thickness and contour could be distinguished on lateral-view laryngeal radiographs; however, thickness measurements made from radiographs did not correlate accurately with actual thickness measurements made at necropsy.