Abstract: Flowheads are described for use in expiratory flow measuring equipment. They are designed to be disposable and to fit on the casing of a unit containing a pressure transducer and associated electronics. The pressure transducer is placed, when the unit is fitted to the casing, in communication with ports (8 and 9) in the wall of a main tube, which ports are respectively upstream and downstream of a central perforated wall (5) which constitutes a passage restriction and across which a pressure drop is accordingly generated if breath is exhaled through the tube. Low pressure drop hydrophilic filters may be used to damp high frequency pressure oscillations and to protect the instrument from ingress of condensed water vapour.