Respiratory disease and subclinical pulmonary abnormalities are recognised complications of both coeliac disease (CD) and inflammatory bowel disease (IBD) but the pathogenesis of the lung disease remains uncertain. We have studied lung function, including permeability measured by clearance of inhaled technetium-99m diethylene triamine pentaacetic acid in 25 patients with IBD, 18 patients with CD on a gluten-free diet, and in 20 normal controls, all without respiratory symptoms. In IBD there was evidence of obstruction to airflow (mean forced expiratory volume in 1 s/forced vital capacity equals 75.8%, control 81%; p less than 0.05) but no change in pulmonary permeability (half-time clearance equals 70.3 vs. 69.2 min). In CD airflow was not significantly different from control (forced expiratory volume in 1 s/forced vital capacity equals 80%) but there was an increase in pulmonary permeability (half-time clearance equals 48.9 min; p less than 0.01). These findings suggest that the mechanisms of lung disease in CD differs from that in IBD and supports the hypothesis of a common mucosal defect in lung and small intestine in CD allowing increased permeability.