Spirometry and regional function studies using 99m-Technetium were performed preoperatively to predict postoperative pulmonary function change in 34 patients who had various pulmonary resectional procedures at the Department of Thoracic and Cardiovascular Surgery, Seoul National University Hospital. Between two months and fourteen months postoperation all the patients were reinvestigated with spirometry and clinical examination to evaluate their functional respiratory status. The postoperative obtained values, especially forced vital capacity [FVC] and forced expiratory volume in one second [FEV1] among the other parameters were compared with the postoperative predicted values. Estimated values of FVC and FEV1 derived from preoperative spirometry and quantitative perfusion lung scan correlated well with the measured postoperative values. The linear regression line derived from correlation between postoperative estimated[X] and postoperative measured[Y] values of FVC and FEV1 in all patients are as follows; 1. Y=0.76x + 0.39 in correlation of FVC [r=0.91] 2. Y=0.88x + 0.17 in correlation of FEV1 [r=0.96],br> This method of estimation was one of the best methods of predicting postoperative pulmonary function change and valuable in determining the extent of safe resection and postoperative prognosis to a poor risk patient with chronic obstructive lung disease.