BACKGROUND There is much anecdotal evidence in Eastern and Western literature describing considerable benefits for patients with asthma when treated with breathing interventions. The term 'breathing exercise or training' has numerous interpretations depending on the nature of the therapy, therapist and cultural background. OBJECTIVE The objective of this review was to assess the evidence for the effectiveness of breathing re-training in the treatment of patients with asthma. METHODS Trials were searched for in the Cochrane Airways Group trials register, Cochrane Complementary Medicine Field trials register, EMBASE: Physical Medicine & Rehabilitation Field, and Databases of the physiotherapy library of current research, World Congress of Physical Therapy Proceedings (1995) and AMED (Allied & Alternative Medicine). Hand searching of the Association of Chartered Physiotherapists in Respiratory Care Journals was undertaken. Chartered physiotherapists in the field of respiratory medicine were contacted and appeals made in the 'Physiotherapy' Journal and the Physiotherapy Respiratory Care magazine. METHODS Randomised or quasi randomised controlled trials of breathing re-training in patients of all ages with a diagnosis of asthma. Breathing re-training should be a major component of the treatment intervention. METHODS Two reviewers (EH & FR) independently assessed trial quality and extracted data. Study authors were contacted for additional information. Information on adverse effects was collected from the included trials where possible. RESULTS Abstracts were identified and 32 full text papers were obtained for assessment and possible inclusion of studies in the review. Twenty seven papers were excluded. A total of five papers were included in this review. Most were small. One large study (106 patients) showed an improvement in PEFR and reduction in rescue bronchodilator use. Otherwise benefit of breathing exercises was found in isolated outcome measures in single small studies. CONCLUSIONS No reliable conclusions can be drawn concerning the use of breathing exercises for asthma in clinical practice.