The development of spirometric airflow obstruction may be a diagnostic dilemma in recipients of single lung allografts. The contribution of bronchial anastomotic stenosis to the observed spirometric obstruction may be clinically difficult to distinguish from that of obliterative bronchiolitis. Similarly, differentiating the "normal" obstructive defect after single lung transplantation for emphysema from obliterative bronchiolitis may be clinically challenging. We retrospectively reviewed the maximum inspiratory and expiratory flow-volume loop contours of lung transplant recipients with either obliterative bronchiolitis (n = 7) or bronchoscopically diagnosed severe bronchial anastomotic stenosis (n = 3). Five patients underwent single lung transplantation for obstructive native lung diseases and underwent observation before and after development of obliterative bronchiolitis. Bronchial anastomotic stenosis-maximum inspiratory and expiratory flow-volume loops were analyzed both before and after correction of stenosis by niobium: yttrium-aluminum-garnet laser photoresection or endobronchial silicone stent placement. Measures of airflow derived from maximum inspiratory and expiratory flow-volume loops, such as peak expiratory flow, peak inspiratory flow, forced expiratory flow at 50% vital capacity, forced inspiratory flow at 50% vital capacity, and forced expiratory volume in 1 second/peak expiratory flow ratio could not differentiate patients with bronchial anastomotic stenosis versus obliterative bronchiolitis. The most clinically useful index was the maximum inspiratory and expiratory flow-volume contour, which was characterized by terminal plateaus during exhalation and inhalation in patients with bronchial anastomotic stenosis. This index was reflected in a lower forced inspiratory flow at 75% vital capacity and forced inspiratory flow at 75% vital capacity/peak inspiratory flow ratio in bronchial anastomotic stenosis that increased after elimination of the anastomotic obstruction.(ABSTRACT TRUNCATED AT 250 WORDS)