We measured pulmonary epithelial permeability in 17 non-smoking patients with generalized bronchiectasis, of whom six had cystic fibrosis, by determining the half-time clearance from lung to blood (T1/2LB) of inhaled 99mTc-labelled diethylene triamine pentaacetate. Their age range was 15-79 years and the range of their FEV1 measurements was 20-87% of the predicted normal. Sputum obtained by prestudy chest physiotherapy revealed significant colonies of Pseudomonas aeruginosa in six, Haemophilus influenzae in three, Staphylococcus aureus in three and Pasteurella mitocida in one patient, while in the remainder there was normal flora only. Lung clearance was significantly faster in the 13 culture-positive patients (mean T1/2LB = 28 minutes) compared with the four culture-negative patients (mean T1/2LB = 54 minutes). There was no correlation between T1/2LB and prestudy FEV1. The study was repeated in six patients following a course of antibiotics. In two patients only was the sputum cleared of organisms and in those the lung permeability decreased significantly. There was no change in lung permeability in the four patients in whom it was impossible to eradicate the sputum organisms. Thus, in our patients with generalized bronchiectasis, lung permeability was increased only in those with both purulent sputum and significant colonization of the respiratory tract by bacterial pathogens. However, this increase in lung permeability was not associated with worse lung function.