In 35 patients with pectus excavatum (aged 17.9 +/- 5.6 years) pulmonary function and maximal exercise test results were compared before and at 1 year after operation. The lower posteroanterior chest diameter on the lateral x-ray film was significantly smaller than normal (p < 0.0001) and increased significantly after operation (p < 0.0001). Preoperatively, total lung capacity (86.0% +/- 14.4%; p = 0.0001) and inspiratory vital capacity (79.7% +/- 16.2; p = 0.0001) were significantly smaller than predicted and further decreased after operation (-9.2% +/- 9.2%; p = 0.0001 and -6.6% +/- 10.7%; p = 0.0012, respectively). Arterial blood gas values displayed normal patterns with increasing exercise both before and after operation. Only the arterial pH decreased more after operation than before (p = 0.0026). After operation there was a significant increase in maximal oxygen uptake (oxygen uptake; p = 0.0002 and oxygen uptake per kilogram; p = 0.0025) and oxygen pulse (oxygen uptake/heart rate approximates an indirect parameter for stroke volume; p = 0.0333) during exercise, whereas the maximal work performed was unchanged. Efficiency of breathing (ratio of tidal volume/inspiratory vital capacity) at maximal exercise improved significantly after operation (p = 0.0005). Ventilatory limitation of exercise (defined by an increase in carbon dioxide tension during exercise) was found in 43.9% of the patients before operation. A tendency of improvement was noted (not significant) after operation (difference in carbon dioxide tension 0.6 +/- 0.4 kPa before versus 0.3 +/- 0.5 kPa after operation). However, the group with normal preoperative carbon dioxide elimination had a ventilatory limitation of exercise after operation (difference in carbon dioxide tension -0.4 +/- 0.3 kPa before versus -0.1 +/- 0.3 kPa after operation; p = 0.0128) with a significant increase in oxygen consumption (p = 0.0007). In conclusion the subjective physical improvement after operation is not explained by changes in cardiorespiratory function at exercise. The data suggest a higher work of breathing after operation.