This study was designed to investigate the regulatory mechanisms of the mucosal microvascular network in the upper respiratory tract. Tracheal mucosal circulation was observed using a specially constructed chamber that allowed direct microscopic visualization of mucosal arterioles. Solutions of increasing hypertonicity (500 and 900 mOsm) applied to the tracheal epithelium resulted in increasing dilation of the underlying mucosal arterioles (p < 0.001). N^omega-nitro-L-arginine methyl ester (L-NAME, 1 mmol/L), a specific inhibitor of nitric oxide synthesis, added to a hypertonic solution inhibited dilation of mucosal arterioles (p < 0.001). Addition of the substrate for nitric oxide synthesis, L-arginine (0.6 mmol/L) to the hypertonic solution containing L-NAME resulted in dilation of mucosal arterioles once again. These data demonstrate that nitric oxide is a crucial mediator in the response of mucosal arterioles to the hypertonic stimulus presented to the epithelial surface of the trachea. Further elucidation of the control of the mucosal microcirculation in the upper respiratory tract could be implemented in new treatment for pathologic processes of the upper respiratory tract such as mucosal congestion and edema