Purpose: The purpose of this study was to investigate the activation of the respiratory centers during insufflation of the larynx with CO2 at different flow rates and concentrations. Materials and Methods: The experiments were carried out in spontaneous air breathing rabbits, anesthetized with thiopental sodium (25 mg kg(-1) i.v.). The larynx was separated from the oropharyngeal cavity and the trachea. The tidal volume (V-T) and respiratory frequency (f min(-1)) were recorded from the lower tracheal cannula. The respiratory minute volume (V-E) was calculated, the action potentials from the right phrenic nerve were recorded and the inspiratory (T-I) and expiratory (T-E) periods and the mean inspiratory flow rate (V-T/T-I) were calculated. The larynx was insufflated at flow rates of 500 mL min(-1) and 750 mL min(-1), with 7 and 12% CO2-Air by means of a respiratory pump. Results: Insufflation of the larynx, with both gas mixtures, decreased the f and VT significantly. The T, and TE were found to increase significantly due to the decreasing in f. There was a significant decrease in V-T/T-I ratio. Following bilateral midcervical vagotomy, on the passing of both gas mixtures, significant decreases were observed in the VT, and the responses of f, T, and TE were abolished. After cutting the superior laryngeal nerve, the responses of the VT to both gas mixtures were abolished. Conclusion: In conclusion, the results of this study purpose that the stimulation of the laryngeal mechanoreceptors by the effect of hypercapnia decreases the activation of the respiratory center.