Bronchial responsiveness has been evaluated in patients with chronic lung congestion secondary to mitral valve disease. Methacholine bronchial challenge was performed by intermittent aerosol generation in 31 patients with mitral valve disease, 18 in New York Heart Association (NYHA) Class II and 13 in NYHA Class III, non-atopic and with baseline forced expiratory volume in one second/vital capacity (FEV1/VC) greater than 85% of predicted and in 30 normal controls. Haemodynamic data were available in 17 patients. The methacholine bronchial provocation dose causing a 35% fall of airway conductance (PD35sGaw) was significantly lower in patients (507 +/- C.I. 205 micrograms) than in normals (2779 +/- C.I. 358 micrograms), (p less than 0.001). In patients log PD35sGaw was significantly correlated with mean pulmonary artery pressure (r = 0.53, p less than 0.05), mean pulmonary capillary wedge pressure (r = 0.67, p less than 0.01), but not with any spirometric parameters. Bronchial hyperresponsiveness seems to be common in patients with mitral valve disease and evidence of lung congestion.