There are many potential problems with the use of serial peak expiratory flow (PEF) measurement to investigate potential occupational asthma. Among these are inaccurate and incomplete recording of results. However, PEF meters will continue to be used because of their relatively low cost and the availability of improved graphing methods and computer-assisted interpretation (OASYS-2). New technologies that automatically record PEF values and the time at which the maneuver was performed have improved the reliability of serial PEF measurements. Further, new hand-held spirometers not only record the test time but also the FEV&inf1; and FEV&inf6;, in addition to PEF. Automated assessment of maneuver quality with immediate feedback to the worker may improve test quality. The storage of raw volume-time or flow-volume curves, not yet widely available, can be used by reviewers to evaluate the quality of the maneuver on which PEF and FEV&inf1; values are based-further improving the reliability of serial measurements. Mechanical stimulators and testing waveforms are available to thoroughly test these new devices and insure that they meet the minimum ATS requirements for monitoring devices.