Abstract: An apparatus for measuring the airways resistance of a person by short-time occlusion of inhalation, includes a face mask having an inlet channel and an outlet channel, the latter provided with an outlet valve, and a narrow passage close to a plenum in front of the face. A pneumotachograph is mounted in the narrow passage and is connected to indicating and recording instrumentation. An elastic balloon filled with a liquid is positioned in the inlet channel and is configured to be fully inflated until total occlosure of the inlet channel and to be completely deflated to allow free air passage therethrough. Inflation and deflation of the balloon is manually performed by means of a syringe which is connected to the balloon by flexible tubing, with both syringe and tubing filled with liquid.