The assumption that the assessment of forced expiratory flow between 25% and 75% of vital capacity (FEF 25-75 ) does not provide additional information in asthmatic children with normal FEV 1 percent predicted has not been adequately tested.We sought to determine whether the measurement of FEF 25-75 percent predicted offers advantages over FEV 1 percent predicted and FEV 1 /forced vital capacity (FVC) percent predicted for the evaluation of childhood asthma.This is a secondary analysis of data from the Pediatric Asthma Controller Trial and the Characterizing the Response to a Leukotriene Receptor Antagonist and Inhaled Corticosteroid trials. Pearson correlation coefficients, Pearson partial correlation coefficients, canonical correlations, and receiver operating characteristic (ROC) curves were constructed.Among 437 children with normal FEV 1 percent predicted, FEF 25-75 percent predicted, and FEV 1 /FVC percent predicted were (1) positively correlated with log 2 methacholine PC 20 , (2) positively correlated with morning and evening peak expiratory flow percent predicted, and (3) negatively correlated with log 10 fraction of exhaled nitric oxide and bronchodilator responsiveness. Pearson partial correlations and canonical correlations indicated that FEF 25-75 percent predicted was better correlated with bronchodilator responsiveness and log 2 methacholine PC 20 than were FEV 1 percent predicted or FEV 1 /FVC percent predicted. In the ROC curve analysis, FEF 25-75 at 65% of predicted value had a 90% sensitivity and a 67% specificity for detecting a 20% increase in FEV 1 after albuterol inhalation.FEF 25-75 percent predicted was well correlated with bronchodilator responsiveness in asthmatic children with normal FEV 1 . FEF 25-75 percent predicted should be evaluated in clinical studies of asthma in children and might be of use in predicting the presence of clinically relevant reversible airflow obstruction.