Inclusion of a standardized measurement of airway function is important in epidemiologic studies of asthma to facilitate comparison between different studies. Bronchial reactivity is widely used in such studies, but measurement of peak expiratory flow (PEF) variability has a number of potential advantages. We compared PEF variability with methacholine challenge tests in a community population sample. Subjects selected at random (n = 95) and on the basis of having experienced wheeze in the last 12 months (n = 130) performed a challenge test with methacholine to a maximum dose of 12.25 mumol and made serial PEF recordings every 2 h for a week. PEF variability was expressed as mean daily maximum amplitude as a percentage of the mean (amplitude % mean). Increased bronchial reactivity and PEF variability were arbitrarily defined as values above the 10th or below the 90th percentiles in the random sample. A measurement of amplitude % mean was available from all 225 subjects, whereas only 115 (51%) had a measurable PD20 methacholine. PD20 measurements correlated weakly but significantly with amplitude % mean (r = -0.44, p less than 0.001). Increased values of both bronchial reactivity and PEF variability were related to the presence of respiratory symptoms in the week before testing. Asthma was more strongly related to increased bronchial reactivity than to PEF variability. Both measurements showed a strong association with atopy and the intraclass correlation coefficients (ratio of between-subject to total variance) were similar for both.(ABSTRACT TRUNCATED AT 250 WORDS)