BACKGROUND: Portable devices for measuring peak expiratory flow(PEF) are now of proved value in the diagnosis and management of asthma and many lightweight PEF meters have become available. However, it is necessary to determine whether peak expiratory flow rate(PEFR) measurements measured with peak flowmeters is accurate and reproducible for clinical application. The aim of the present study is to define accuracy, agreement, and precision of mini-Wright peak flow meter(MPFM) against standard pneumotachygraph. METHODS: The lung function tests by standard pneumotachygraph and PEFR measurement by MPFM were performed in a random order for 2 hours in 22 normal and 17 asthmatic subjects and also were performed for 3 successive days in 22 normals. RESULTS: The PEFR measured with MPFM was significantly related to the PEFR and FEV1 measured with standard pneumotachygraph in normal and asthmatics(for PEFR, r=0.92 p<0.001; for FEV1, r=0.78 ; p<0.001). The accuracy of MPFM was within 10%(limits of accuracy recommeded by NAEP) in all the subjects or 22 normal, mean difference from standard pneumotachygraph being I 6.5L/min(percentage of difference being 2.90%) or 1 0.6L/min(percentage of difference being 1.75%), respectively. According to the method proposed by Bland and Altman, the 95% limits of the distribution of differences between MPFM and standard pneumotachygraph after correction of PEFR using our regression equation were +38.2 and -71.5L/min in all the subjects or -20.49~ + 9.49L/min in 22 normal and was similar to the intraindividual agreements for 3 successive days in normal. There was no statistically significant difference of PEFR measured with MPFM and standard pneumotachygraph among three days(p>0.05) and the coefficient of variation(2.4 1.2%) of PEFR measured with MPFM was significantly lower than that( 5.2 3.5%) with standard pneurnotachygraph in normal (p<0.05). CONCLUSION: This results suggest that the MPFM was as accurate and reproducible as standard pneumotachygraph for monitoring of PEFR in the asthmatic subjects.