Every year, an increasing number of people travel to high altitude and travellers with asthma are becoming more common in remote environments.1 It is well recognised that certain situations at high altitude, such as exercising in cold air, may provoke symptoms.2 However, the mountain environment offers a reduced pollutant and allergen load, potentially causing fewer exacerbations.3 Additionally, increased sympathetic tone and adrenocortical output caused by hypoxia counteract bronchospasm. Acetazolamide, used widely by trekkers for the prophylaxis of acute mountain sickness (AMS), has an additional benefit in patients with asthma of reducing airway hyperreactivity.4 To our knowledge, this is the first prospective …