A study of the relation between physical signs and the clinical and physiological pattern of chronic lung disease with obstruction has been carried out on 24 patients with varying degrees of airways obstruction. One sign (the forced expiratory time) was a direct reflection of the obstruction, but a number of other signs which also correlated significantly with the specific airway conductance were probably related to secondary effects on lung volume (increased resonance), disordered pattern of muscle action (tracheal tug and use of accessory muscles) or to excessive swings of intrathoracic pressure (excavation of supraclavicular fossae). Other signs which are regularly present but which did not correlate significantly with the severity of the airways obstruction were often related to other factors such as age or duration of symptoms (tracheal length). The difficulties in deciding the origin of other signs such as wheezes (rhonchi) or costal paradox are discussed.