Pulmonologists routinely use pulmonary function tests (PFTs) to help guide their care of patients with respiratory disease. Spirometry is the most commonly used PFT because it is simple and reproducible. The introduction of computerized spirometers has led to PFT reports containing multiple parameters. Because small airway obstruction is an early feature of many obstructive lung diseases, such as asthma, cystic fibrosis, and bronchiolitis obliterans, it is desirable to identify parameters that reflect flows in this area of the respiratory system. In this regard, both the forced expiratory flow at 50% of vital capacity (FEF50) and forced expiratory flow at 25 to 75% of vital capacity (FEF25–75) have been considered to more closely reflect small airway flow.1–2 How should a clinician decide which of these parameters is most helpful in assessing lung function? In this issue of CHEST (see page 731), Bar-Yishay et al compare FEF50 and FEF25–75 to provide some answers to this question by reviewing the spirograms of 1,350 children followed up at their center. They found that the two measures correlated very well, and that the FEF50/FEF25–75 ratio remained constant even in the setting of severe obstruction. To decrease the number of unnecessary parameters in spirometry reports, they recommend reporting the FEF50 only, because it is directly measured rather than calculated using an algorithm and shows less variability.