Pulmonary rehabilitation has become an evidence-based treatment for patients with severe chronic obstructive pulmonary disease (COPD). However, large numbers of patients who suffer from mild to moderate COPD receive treatment from their general practitioners (GPs). To encourage compliance, advice given to patients in general practice should be clear, practical, and acceptable. This is particularly true of the advice that is given by GPs to improve their patients' physical condition by walking, cycling or swimming, as recommended by the Dutch College of General Practitioners in their guideline for the treatment of COPD. We performed a literature search on the effects of physical activity in patients with mild to moderate COPD on exercise tolerance, dyspnoea and quality of life (QOL). We also looked at the numbers of hospitalisation days and exacerbations, expressed as oral prednisolone courses. The literature search included Medline (1983 to 1999), EMBASE (1984 to 2000), and the Cochrane Library (2000). All hits were screened for subject and language and abstracts were selected on the basis of a protocol that included disease severity, hypothesis, outcome parameters, and control group. Review articles on physical exercise and COPD were examined and reference lists of selected articles were screened for relevant studies The broad literature search generated 4,968 articles and, after exclusion according to title and abstract, 35 original studies and 27 review articles were analysed. Of these, five original studies fitted the criteria and none of the review articles was selected. A positive influence of physical activity on exercise tolerance in mild to moderate COPD was reported in four out of five studies. There was no clear effect on dyspnoea or QOL, probably because of the low numbers of subjects. No studies that addressed the number of hospitalisation days or prednisolone courses as outcomes were included. Physical exercise training (usually as part of a package of rehabilitation) can improve the fitness of patients with mild or moderate COPD, but it has not been shown to benefit QOL or dyspnoea significantly, or indeed long-term disease progression.