Objective: A prospective study was carried out to find the exact site of obstruction in sleep model and to quantitatively evaluate the effect of Jaw-thrust maneuver (JTM) in opening the obstructed airway using flexible fiberoptic endoscope. Methods: Twenty-eight ASA physical status I or II patients with snoring symptom undergoing elective surgery were included. The patients were held in supine position without hyperextension of the neck. Having induced anesthesia, the base of the tongue and laryngeal inlet and/or epiglottis were visualized using endoscope. The patients' epiglottides were classified as leaf-shaped, curved (concaved or omega-shaped) and floppy types. We graded the airway opening at the level of epiglottis into six grades and obstruction at the tongue base level into four grades. The grades during inspiration (GrIns), expiration (GrExp) and after JTM (GrJTM) were recorded and compared with Pearson chi-square test. Results: The strictly curved (Omega-shaped or concaved) epiglottis supplied a salvage pathway for airflow that resisted collapsing with the posterior movement of the tongue base in 2 patients. When we compared GrIns with GrExp for epiglottis the difference was statistically significant (chi(2) = 0.001), but the difference for tongue base was not (chi(2) = 0.152). After JTM, GrJTM for both epiglottis and tongue base were significantly better than GrIns and GrExp (chi(2) ! 0.001). Conclusion: Tongue base was the principal site of obstruction although during the respiratory cycle the position of epiglottis changed prominently and increased the obstruction in inspiration. JTM alone significantly relieved the obstruction at the tongue base and epiglottis levels and increased the retroglossal airway. Copyright (C) 2005 S. Karger AG, Basel.