There is controversy over whether children in developing countries can catch up on their growth rates after bouts of diarrhoea. A factor influencing catch-up growth is the extent and duration of mucosal injury. To explore the relation between intestinal disease and growth performance, a non-invasive test of intestinal integrity, the lactulose:mannitol permeability test, was done regularly on children aged 2-15 months, whose growth was monitored over a mean of 7.5 months. The study revealed persistent abnormalities in the small bowel mucosa of 2-15 month old Gambian infants and a negative correlation between these abnormalities and growth. Up to 43% of observed growth faltering can be explained on the basis of these long-term intestinal lesions.