We investigated the impedance of excised preparations of the human larynx before and after resection of the vocal cords and of the trachea whether or not in connection with the main bronchi for steady (75-700 ml.s-1) and oscillatory flows (4-64 Hz). To simulate the influence of respiratory flow on oscillatory resistance (Rosc), oscillatory and steady flow were superimposed. This resulted in a marked increase of Rosc, dependent on the value of steady flow, a change of the frequency dependence of Rosc, and a decrease of the reactance. The latter effects were particularly pronounced in the preparations of the larynx, especially with a narrow glottis opening. The influence of steady flow on oscillatory resistances is probably the expression of interactions of steady and oscillatory flow regimes in the larynx. Similar but less pronounced interactions are also met in the trachea. These effects lead to a systematic overestimation of upper airway resistance when measured during spontaneous breathing by means of a forced oscillation technique.