The mechanisms for exercise intolerance in chronic obstructive pulmonary disease are complex and multifaceted. Although ventilatory limitation caused by abnormal pulmonary function is a major contributor to this phenomenon, other factors may play an important role in limiting exercise. These other factors include depressed cardiac function, respiratory and peripheral muscle weakness, nutritional imbalances, and psychologic factors. The assessment of the pulmonary patient who complains of decreased functional status must include examination and consideration of all these variables. Only by addressing and treating the combination of these variables as they present in an individual patient will clinicians have the potential to impact that individual's functional status and quality of life.