Pulmonary function and respiratory muscle strength was assessed in 20 patients with mitral stenosis uncomplicated by other illness. Pulmonary function was evaluated by spirometry, flow-volume curves, functional residual capacity (FRC) and total lung capacity (TLC). Respiratory muscle strength was evaluated by measurement of maximal static inspiratory and expiratory mouth pressure (PIM, PEM cmH2O) at FRC and TLC respectively. Spirometric, FRC and TLC average values were normal. The maximal expiratory flow rate at 50 and 25% of vital capacity were decreased to 49.5 and 38.3% from predicted values. The values of PIM and PEM in patients (-93 +/- 17; 128 +/- 32 cmH2O, respectively) were similar to those of 12 normal subjects studied at comparable lung volume. Our results were similar to previous reports. There was no evidence of decreased respiratory muscle force, probably because the patients nutritional status and cardiac output were normal.