This investigation studied the effect of two intravenous benzodiazepines and the specific reversal agent, flumazenil, on the sensitivity of upper airway reflexes. In a blinded, randomised, crossover study, we have investigated the effect of a single dose of diazepam ('Diazemuls') (0.2 mg.kg-1) and midazolam (0.07 mg.kg-1), both given intravenously on the sensitivity of upper airway reflexes in eight male volunteers. Reflex sensitivity was assessed by identification of reflex glottic closure in response to a threshold concentration of inhaled ammonia vapour. Both diazepam and midazolam produced significant depression of upper airway reflex sensitivity. This was maximum with both drugs within 10 min of administration, but baseline sensitivity was regained within 60 min. Flumazenil (300 micrograms) administered 10 min after midazolam, resulted in significant reversal of the upper airway reflex sensitivity depression.