Rehabilitation is not a type of treatment: it is the condition of optimal function, or the achievement of that condition. Pulmonary rehabilitation is simply a function-orientated approach to the clinical management of the patient with chest disease. It starts with the best available conventional treatment and then proceeds with any modality which might enhance the patient's level of physical, mental, or social function. The emphasis in this review has been on measures to increase exercise capacity, in particular, possible mechanisms whereby exercise training may benefit the patient with chronic airflow obstruction. It is hoped that the comments will lead to further studies in this area, and encourage doctors to think beyond the mere treatment of chest disease, to the attainment of the best possible level of function despite the presence of chest disease.