The European Community Respiratory Health Survey (ECRHS) II is a multicenter study that assesses bronchial responsiveness using the Mefar™ dosimeter. WARD et al. reported significant variation in dosimeter driving pressure across participating centers, ranging from 70 to 245 kPa, which could confound between-center comparisons of bronchial hyperresponsiveness. To address this issue, all ECRHS II centers were instructed to check and adjust dosimeter driving pressure monthly, with readings outside the manufacturer's specification (180 ± 5%) requiring adjustment. Despite the initial concerns, the quality control program revealed that while variations exist, their magnitude and influence on between-center comparisons are smaller than previously suggested. The mean pressure ranged from 160 to 189 kPa, with Hamburg having a higher mean due to a period of higher driving pressure. The authors conclude that the quality control program has validated its value in ensuring data reliability.The European Community Respiratory Health Survey (ECRHS) II is a multicenter study that assesses bronchial responsiveness using the Mefar™ dosimeter. WARD et al. reported significant variation in dosimeter driving pressure across participating centers, ranging from 70 to 245 kPa, which could confound between-center comparisons of bronchial hyperresponsiveness. To address this issue, all ECRHS II centers were instructed to check and adjust dosimeter driving pressure monthly, with readings outside the manufacturer's specification (180 ± 5%) requiring adjustment. Despite the initial concerns, the quality control program revealed that while variations exist, their magnitude and influence on between-center comparisons are smaller than previously suggested. The mean pressure ranged from 160 to 189 kPa, with Hamburg having a higher mean due to a period of higher driving pressure. The authors conclude that the quality control program has validated its value in ensuring data reliability.