Background The variability of peak expiratory flow (PEF) is now commonly used in the diagnosis and management of asthma. It is essential for PEF meters to have a linear response in order to obtain an unbiased measurement of PEF variability. As the accuracy and linearity of portable PEF meters have not been rigorously tested in recent years this aspect of their performance has been investigated. Methods The response of several portable PEF meters was tested with absolute standards offlow generated by a computer driven, servo controlled pump and their response was compared with that of a pneumotachograph. Results For each device tested the readings were highly repeatable to within the limits of accuracy with which the pointer position can be assessed by eye. The between instrument variation in reading for six identical devices expressed as a 95% confidence limit was, on average across the range of flows, ±8-5 1/min for the

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The feasibility of routinely monitoring the use of rehabilitation devices was successfully demonstrated and production development is now being undertaken.

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