Spirometry can be performed in GPs' surgeries but test quality and accuracy of interpretation are uncertain. To test the feasibility and usefulness of specialist on-line reporting of spirometry in general practices. Six randomly selected practices (6000+ patients) were provided with a spirometer, training, and workload reimbursement. Each practice did tests on at least 50 patients in whom abnormal results were expected. Test results were given to a practice clinician and to the local respiratory unit for interpretation. Written reports from both were compared to assess primary care interpretation of test quality, and diagnosis. Disagreements between primary and secondary care assessments were reviewed by a multidisciplinary team. Those of clinical importance were included in the analysis. 29 of 44 practices wanted to take part. In the six selected practices 312 tests were completed. Mean age was 64 years (19–94 yrs), 52% female, mean predicted FEV1 69% (16–127%). 77 of 185 tests reported as acceptable in primary care were judged unacceptable by the specialist. 136 tests were judged obstructive by the specialist of which 85 were identified as obstructive by the primary care teams. In 129 of 218 (59%) tests there was complete agreement about level of severity. Practices differed in the frequency of disagreement with the specialists but in all there were disagreements in more than 15% of tests. Online reporting of primary care spirometry is feasible and primary care teams are interested in it. The level of disagreement between primary care and specialist interpretation of the tests suggests that specialist reporting of tests is essential in these practices if primary care spirometry is to be carried out to an acceptable standard. Conflict of interest and funding Research Support Unit of Southwark Primary Care Trust, London.