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Measurement of the rate of flow of air during inspiration is important in respiratory physiology and for the design of protective respiratory devices. Methods that have been used previously are described and their limitations explained. A new instrument was constructed for such measurements, which offers no appreciable resistance to air flow. This instrument consists of a microscopic platinum wire suspended across the diameter of a 31.6‐mm tube. One end of the wire is attached to a fixed point and the other end to a fine spring. The displacement of the wire when air flows through the instrument is recorded photographically by a moving paper camera. The deflection of the wire is linear with air flow, and its inertia, lag, and frequency of vibration do not interfere with respiratory measurements. A low resistance valve and mask system complete the apparatus.