To help determine whether preoperative perfusion and inhalation SPECT imagings are useful in predicting postoperative lung function, Tc-99m MAA perfusion SPECT imaging, CT scans, and pulmonary function tests were prospectively performed in 33 patients with primary lung cancer before and after lobectomy or pneumonectomy. Tc-99m Technegas inhalation SPECT imaging was performed in 6 of 33 patients as well. The authors also studied changes in radioactivity on the operated and nonoperated sides before and after surgery, examined the lowest limit value for adaptability to the operation, and made a comparison of both perfusion and inhalation SPECT imaging. The predicted postoperative values obtained from the preoperative Tc-99m MAA SPECT images correlated more closely with the measured 6-month postoperative values than with the measured 3-month postoperative values. The highest correlation coefficient (r = 0.86) was observed between the predicted forced vital capacity (FVC) value and the measured 6-month postoperative FVC value. In many cases, there was not a great difference between the 6-month and 3-month radioactivity on the operated side obtained from Tc-99m MAA SPECT images. This appears to indicate that pulmonary blood flow on the operated side has completely recovered by 3 months after surgery. However, radioactivity in both the upper and lower lobes of the nonoperated side increased soon after surgery compared with that before the operation, and had not returned to preoperative levels 6 months after surgery. The radioactivity in the right middle lobe did not change before and after surgery.(ABSTRACT TRUNCATED AT 250 WORDS)