Wehavestudied alveolar attachments to membranous bronchioles In 41patients enrolled In the National Institutes of Health Intermittent Positive Pressure Breathing Trial who died, came to autopsy, and provided adequate tissue for examination. The patients had moderate to severe chronic airflow obstruction and, on the average, severeemphysema. Wemeasured the number of normal attachments per membranous bronchiole per case (N), the number of normal attachments per mm of circumference per bronchiole per case (Nunit), and the ratio of abnormal to all attachments (R). All measurements correlated closely to all measurements of emphysema and to Irregular shape of bronchioles (deformity Index). Measurement of abnormal attachments correlated with abnormal tests of pUlmonary function, Including evidence of airflow obstruction and diffusing eapaelty for carbon monoxide (Oleo). Nunit showed the most frequent correlations, but both Nand Nunlt were only related independently of emphysema for Phase III of the single-breath nitrogen test. R was related to loss of OLeo. Weconclude that loss of attachments is not itself a cause of airflow obstruction but rather a correlate of emphysema, which Is the proximate cause of the obstruction.