18 patients with severe bronchiectasis and persistent purulent sputum production were investigated, by the use of gamma scans, between acute exacerbations of their symptoms to determine localisation and traffic of 111In-labelled granulocytes in the lungs. Labelled granulocytes appeared in the respiratory tract of 16 patients within 24 h of their injection. Uptake occurred almost exclusively in areas demonstrated by computed tomography (CT) to be bronchiectatic. However, 111In uptake was not demonstrated in 21 of the 55 segments showing bronchiectasis on CT, and these were therefore thought to be not actively inflamed. The whole-body loss of radioactivity up to 4-7 days following injection of the labelled cells ranged from 0 to 53% and correlated with 24 h purulent sputum volume (r = 0.45, p less than 0.01) and with CT extent of moderate and severe bronchiectasis (r = 0.40, p less than 0.05), but not with overall CT extent of bronchiectasis, age, forced expiratory volume in one second, or duration of purulent sputum production in years.