OBJECTIVE To analyze the value of preoperative lung scanning and exercise testing for the prediction of postoperative complications and of the short- as well as long-term performance in lung resection candidates at increased risk for complications. METHODS Prospective clinical trial. METHODS Clinical pulmonary function laboratory in a university teaching hospital. METHODS Twenty-five (mean age, 63 years; 17 men) of 84 consecutive lung resection candidates were considered at increased risk for postoperative complications due to impaired pulmonary function (FEV1 < 2 L or diffusion of carbon monoxide [DCO] < 50% predicted, or FEV1 and DCO < or = 80% predicted combined with New York Heart Association dyspnea index > or = 2). METHODS Candidates underwent radionuclide ventilation/perfusion scans and exercise testing to predict postoperative (= ppo) values for FEV1, DCO, and maximal O2 uptake (VO2max). They all underwent thoracotomy for neoplastic lesions; 7 had pneumonectomies, 18 lobectomies. Six patients had postoperative complications (within 30 days), of whom three died. Three and 6 months postoperatively, pulmonary function tests and VO2max were repeated. RESULTS In the 22 survivors, the observed values were then compared with the predicted values. At 3 months, there were excellent correlations (absolute/predicted values): for FEV1 r = 0.78 and 0.81; for DCO, r = 0.77 and 0.74; and for VO2max, r = 0.71 and 0.83. The means of FEV1 and VO2max did not differ from the predicted values, whereas the predicted DCO was lower than the observed value (mL/min/mm Hg: 15.1 vs 17.9; percent predicted: 59.6 vs 70.9) (p < 0.05). At 6 months, correlations remained very good for FEV1 (r = 0.81 and 0.84) and for DCO (r = 0.76 and 0.74), but had decreased for VO2max to 0.56 and 0.65, respectively. All means were higher than predicted (p < 0.05) owing to recovery in the lobectomy group. Patients with postoperative complications (group B) had a lower preoperative VO2max in percent predicted (62.8 +/- 7.5% vs 84.6 +/- 19.7%) (p < 0.01) and also a lower VO2max-ppo (10.6 +/- 3.6 vs 14.8 +/- 3.5 mL/kg/min and 44.3 +/- 13.5 vs 68.0 +/- 20.7% predicted) (p < 0.05) than patients without complications (group A). A VO2max-ppo < 10 mL/kg/min was associated with a 100% mortality. Although FEV1-ppo and DCO-ppo were lower in group B, the difference did not reach significance. CONCLUSIONS Radionuclide-based calculations of postoperative VO2max are predictive of operative morbidity and mortality: a VO2max-ppo of < 10 mL/kg/min may indicate inoperability. Further, short-term postoperative performance is accurately predicted by FEV1-ppo and VO2max-ppo, but long-term function is underestimated after lobectomy.