Both mandibular advancement (MA) and contraction of the genioglossus (GG) have been shown to improve upper airway patency, but neither one achieves the effect of CPAP treatment. In the present study we assessed the combined effect of MA and GG stimulation on the relaxed pharynx in patients with obstructive sleep apnea (OSA). We evaluated responses of upper airway pressure-flow relationships and endoscopically determined pharyngeal cross-sectional area to MA and electrical stimulation of the GG in 14 propofol-anesthetized OSA patients. Measurements were undertaken at multiple levels of CPAP, enabling calculation of the critical closing pressure (Pcrit), upstream resistance (Rus) and pharyngeal compliance. GG contraction, MA and the combination of both shifted the pressure:flow relationships toward higher flow levels, resulting in progressively lower Pcrit (from baseline of 2.9±2.2 to 0.9±2.5, -1.4±2.9 and -4.2±3.3 cmH2O, respectively), without significant change in Rus. Pcrit during GG stimulation was significantly larger during MA than under baseline conditions (-2.8±1.4 vs. -2.0±1.4 cmH₂O, p=0.011). Combining the effect of GG stimulation with MA lowered Pcrit below 0 in all patients, and restored pharyngeal patency to a level that enabled flow above the hypopnea level in 10/14 of the patients. Velopharyngeal compliance was not affected by either manipulation. We conclude that the combined effect of MA and GG stimulation is additive and may act in synergy, preventing substantial flow limitation of the relaxed pharynx in most OSA patients.