Breathing techniques are used by a large proportion of asthma sufferers. This systematic review was aimed at determining whether or not these interventions are effective. Four independent literature searches identified six randomized controlled trials. The results of these studies are not uniform. Collectively the data imply that physiotherapeutic breathing techniques may have some potential in benefiting patients with asthma. The safety issue has so far not been addressed satisfactorily. It is concluded that too few studies have been carried out to warrant firm judgements. Further rigorous trials should be carried out in order to redress this situation.