Slow inspiratory vital capacity (IVC) and forced expiratory volume in 1 s (FEV1) before and after an inhaled beta-agonist are widely used to detect reversible airflow limitation in patients with chronic obstructive lung disease. The measurement of airways resistance (Raw) during quiet breathing with the body plethysmograph is less frequently used. It may well be of importance in clinical emphysema where measurement of FEV1 is confounded by the collapse of the bronchi, which does not occur when measuring Raw during quiet breathing. We assessed whether Rrs, in addition to IVC and FEV1, can be used to gain a better insight into the reversibility with 400 micrograms of fenoterol in patients with clinical emphysema. We studied a group of 51 patients (9 women and 42 men; mean [+/- SD] age, 64.7 [7.7] years) who had a clinical diagnosis of emphysema. Significant reversibility was identified by spirometry (IVC, FEV1) and body plethysmography (Raw) in 20 patients (39 percent). Inspiratory vital capacity alone identified reversibility of airflow limitation in 11 patients (22 percent). In 5 patients (10 percent), the postbronchodilator improvement was seen exclusively in the Raw measurement. In the remaining patients, absence of improvement in spirometric and plethysmographic parameters was found. Subjective improvement occurred to the same extent in patients whose Raw and IVC improved. We concluded that Raw gives important information about the reversibility of airways obstruction in patients with clinical emphysema. Therefore, we suggest that tests during quiet breathing should be part of the routine examination of airways obstruction in patients with "irreversible" obstruction by conventional spirometry.