More and more general practitioners (GPs) use spirometry in their practices. At this time, there is sufficient reason to presume that, after a single postgraduate training program without any further support, most GPs have insufficient knowledge and ability to assure valid interpretation of their spirometry tests. Therefore, some kind of continuous diagnostic support with regard to spirometry interpretation by GPs is advisable. The aim of the present study is to assess whether implementation of spirometry expert support (either by a computerised expert system or a working agreement between general practitioners and respiratory consultants with respect to spirometry interpretation) causes changes in diagnosing and appropriateness and efficiency of medical care in subjects with chronic respiratory morbidity managed in general practice.