An on-line computerised lung function screening test is described which prints out 22 lung function parameters and a functional diagnosis. The complete test with print-out data takes less than 8 min per patient which implies that more than 60 out-patients can be 'screened' per day. Furthermore, for patients about to undergo major surgery a lung function operative risk grading is also available. The developed computer system is comparatively inexpensive, simple to operate and can be immediately on-lined to most apparatus without special interfacing. The total screening system can be operated by a single technologist and the required respiratory manoeuvres can be performed by almost all patients irrespective of the degree of lung function impairment. Although comprehensive in itself the screening test has been invaluable in deciding upon which patients require more intensive and time-consuming lung function investigations.