The lung function after lung resection was studied in 18 patients using ventilation and perfusion scintigraphy. All patients underwent posterolateral thoracotomy. Scintigraphy was performed before and 1 month after surgery in 8 lobectomized patients and in 4 partially resected ones. Another 8 patients underwent scintigraphy 6.5 to 43 months after lobectomy. Mean transit time (MTT) on scintigraphy was used to estimate a regional washout function in lung. The value of MTT on the operated side minus MTT on the contralateral side increased after surgery. This change was more remarkable in lobectomized patients than in partially resected ones. MTT on the operated side lung was even more prolonged after operation. Reduction of %V and %Q was observed on the operated side of remaining lung after surgery, and Q decreased more than V after lobectomy.