This study was undertaken to investigate the effects of ear canal air pressure variation on the threshold of acoustic reflex. The acoustic reflex threshold was obtained to 500 and 1000 Hz activating signals as pressure was varied between ±200 mm H2O. The results demonstrated a reduction in sensitivity of the acoustic reflex with variations in positive or negative air pressure. Observation of the conductance component of admittance consistently required higher intensity levels to elicit the acoustic reflex. Clinical implications are that external air pressure can vary within a range of ±80 mm H2O and continue to maintain the acoustic reflex threshold close to its value obtained at maximum compliance.