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 problem formulation for the study proposed is: "Does implementation of spirometry expert support (either by a computerized expert system or a local working agreement between GPs and respiratory consultants with respect to spirometry interpretation) cause changes in diagnosing and quality and efficiency of medical care in subjects with chronic respiratory morbidity managed in general practice?”. In order to address this issue, two separate studies with different designs are proposed. Study I (n=62 GPs) is an ‘in-depth’ study of the GPs‘ decision-making process with regard to spirometry, and the impact of a computerized expert system on this process. Study II (n=39 general practices) is a pragmatic randomised-controlled implementation study evaluating two realistic modes of spirometry expert support (i.e., a computerized expert system or a working agreement between GPs and respiratory consultants).