Intestinal permeability was investigated in 16 children with cystic fibrosis and 14 age-matched controls, making use of 51Cr-EDTA as probe molecule. Orocecal transit time was also evaluated using the lactulose/hydrogen breath test. There was an increase in permeability to 51Cr-EDTA in patients with cystic fibrosis (mean 13.62%) compared with the control group (mean 1.08%). The orocecal transit time was prolonged in patients with cystic fibrosis compared with controls. Mean fasting breath hydrogen concentration was significantly greater in cystic fibrosis patients (13 ppm) compared with control patients (3 ppm). There was no correlation between the percentage of 51Cr-EDTA excreted and the orocecal transit time in either control or cystic fibrosis patients.