The purpose of this study is to predict postoperative lung function by perfusion lung scanning method. 40 patients who underwent lobectomy or pneumonectomy between 1983-1985 were analyzed. Mean preoperative FEV1 was 2.36 L in lobectomy cases and 1.73 L in pneumonectomy cases. Preoperative and postoperative lung function were measured by routine spirometry in sitting position. Perfusion lung scanning was performed by 99mTc-MAA radioisotope. Postoperative FEV1 and VC were predicted by the formula; Postoperative FEV1 [VC]=Preoperative FEV1 [VC] x percent function of regions of lung not to be resected. In this study, I concluded that perfusion lung scanning is a simple and useful method to predict postoperative ventilatory function after pneumonectomy of lobectomy.