Health professionals recommend education of patients about COPD. There is no satisfactory instrument to measure their knowledge and therefore to assess the results of education. A multiple-choice questionnaire (BCKQ) has been designed and tested. Each of 13 topics contains five statements for which there is a right or wrong answer. Its validity and consistency has been assessed, and the test re-test reliability and responsiveness measured after an interval of eight weeks. A copy of the multiple-choice questionnaire is given in the Appendix. The questionnaire was judged by patients and health professionals to have good content and face validity. It has good internal consistency for the 65 items. (Cronbach's alpha 0.73). It can be completed and scored within twenty minutes. The average score in subjects who had not received prior education was 54.7%. In a group not receiving education there was good test-retest reliability (r = 0.71). Following an eight-week education programme there was a significant improvement of 18.3 percentage points, and most of the increase was maintained for six months without any further formal education. BCKQ is suitable for both clinical and research purposes. It will test knowledge that is appropriate for COPD patients and can be used as an assessment tool for individual patients, or as a broad cross-sectional survey instrument. It will enable the effectiveness of education to be assessed and will be of value in developing and comparing different educational interventions.