In an attempt to compare most of the available pulmonary function tests in detecting airway obstruction after exercise, two studies were conducted. In the first study 24 bronchodilator-dependent asthmatic boys were evaluated before treadmill exercise (baseline) and at 7 and 30 minutes afterwards. The following pulmonary function parameters were measured: forced vital capacity (FVC), forced expiratory volume in one second (FEV1), maximum mid expiratory flow (MMEF), peak expiratory flow rate, thoracic gas volume, airway resistance, specific airway conductance (SGaw), and closing volume (CV). Results showed that SGaw, MMEF, and CV were the most sensitive parameters reflecting changes in airway caliber. Less significant changes also appeared in FEV1 and in FVC. The significance of these changes and their relationships to other parameters are discussed. In an attempt to better understand the effects of airway obstruction on the maximum-expiratory flow-volume curve (MMEF curve) after exersise, a second study was conducted. Comparisons were made between "classical" parameters such as MMEF (measured by spirometry), SGaw (measured by body plethysmography), and flow-volume parameters (measured by wedge spirometer). Sixteen asthmatic subjects (9 to 12 years of age) whose airway obstruction was further exacerbated by exercise of a moderate work load on the treadmill (2 w/kg of body weight) were studied. The asthmatic subjects were tested prior to exercise and at 7 and 30 minutes after exercise. All the measurements mentioned above were done in a randomized manner. When both MMEF and SGaw were decreased in the post-exercise period, significant correlations were obtained between these "classical" parameters and all of the flow-volume parameters. However, when only one of the two was decreased, no correlation could be obtained with any of the flow-volume parameters. It was concluded that under certain conditions flow-volume curves reflect airway obstruction satisfactorily, but under other conditions they appear to be less sensitive than the "classic" parameters. These results are also discussed.