Nasal obstruction disturbs comfort during daytime, and sleep quality. Convenient objective assessment of nasal ventilation would be desirable. Therefore, we developed a technique for unobtrusive monitoring of bilateral nasal airflow. Nasal cannulae with separated left- and right-sided tubings were connected to two pressure transducers. Calibration tables were obtained by recording left and right nasal pressures during sequential unilateral nasal occlusion over a few breaths along with airflow by a flow meter attached to a mask. Based on these data, nasal pressures subsequently provided side-selective estimates of airflow without need for a mask. Accuracy of left and right nasal pressure derived airflows was evaluated by comparison of their sum to a flow meter in a bench model, in five volunteers at baseline and during unilateral nasal obstruction by histamine and in five patients during overnight sleep. In the model and volunteers, nasal pressure and flow meter derived flow agreed closely at baseline, and during partial nasal obstruction that altered left/right nasal flow ratios. In patients, nasal pressure derived tidal volumes accurately tracked flow meter estimates over >6 h (70 comparisons, bias -1%, limits of agreement +/-19%). The described method allows continuous, side-selective and unobtrusive monitoring of nasal ventilation for diagnostic evaluation and assessment of treatment effects.