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Purpose: The larynx has a dual role in the regulation of gas flow into and out of the lungs while also establishing resistance required for vocal fold vibration. This study assessed reciprocal relations between phonatory functions--specifically, phonatory laryngeal airway resistance ([R.sub.law])--and respiratory homeostasis during states of ventilatory gas perturbations. Method: Twenty-four healthy women performed phonatory tasks while exposed to induced hypercapnia (high C[O.sub.2]), hypocapnia (low C[O.sub.2]), and normal breathing (eupnea). Effects of gas perturbations on [R.sub.law] were investigated as were the reciprocal effects of [R.sub.law] modulations on respiratory homeostasis. Results: [R.sub.law[remained stable despite manipulations of inspired gas concentrations. In contrast, end-tidal C[O.sub.2] levels increased significantly during all phonatory tasks. Thus, for the conditions tested, [R.sub.law] did not adjust to accommodate ventilatory needs as predicted. Rather, stable [R.sub.law] was spontaneously accomplished at the cost of those needs. Conclusions: Findings provide support for a theory of regulation wherein [R.sub.law] may be a control parameter in phonation. Results also provide insight into the influence of phonation on respiration. The work sets the foundation for future studies on laryngeal function during phonation in individuals with lower airway disease and other patient populations., The larynx, as part of the upper airway, has a challenging dual role in the simultaneous regulation of gas flow into and out of the lungs for respiration as well [...]