In an epidemiological study a random sample (1,554 males aged 35 to 54 years) of the population of a hydrogen chloride air-polluted area was investigated by means of the modified MRC questionnaire and maximal expiratory flow-volume curves. The MEF-values were dependent on age and height. We stated no significant differences between potash miners and the remaining population. In contrast we found significant differences between smokers and non-smokers and also between persons with and without respiratory symptoms. Persons with bronchitis and chronic bronchitis most differed from reference groups in MEF 75 (flow at high lung volume). Comparing smokers with non-smokers MEF 25 attained the highest significance level. In our investigation the maximal expiratory flow-volume curve was only a little more sensitive than conventional spirometry.