Pulmonary function testing (PFT) has been used to evaluate the risk for postoperative complications since the 1950s. PFT including spirometry, lung volumes, diffusing capacity, oximetry, and arterial blood gases has been used to assess the postoperative risk of lung resection. In selected cases, additional evaluation may include radionuclide lung scanning, exercise testing, invasive pulmonary hemodynamic measurements, and risk stratification analysis. A new index, predicted postoperative product (PPP), was found to have strong predictive ability for mortality. We defined a new useful index, measured product (MP), to predict postoperative complications; MP had similar advantages of PPP. Since diffusing capacity at rest has been shown to be a good predictor of postoperative complications following lung resection, and since exercise testing has been also useful in preoperative evaluation prior to lung resection, we reasoned that evaluation of the effect of exercise on diffusing capacity would be helpful to evaluate the ability of the pulmonary capillary bed to expand and increase its capacity to transfer gas during exercise.