Intestinal permeability to sugar has been used as an objective measure of small bowel integrity to assess the efficacy of an elemental diet as the sole treatment or Crohn's disease of the small bowel. Fourteen children aged 11-17 years with active small bowel Crohn's disease were given an elemental diet for six weeks. Investigations with iso-osmolar oral test solutions before and after this treatment showed that all 14 children had abnormally raised lactulose/L-rhamnose permeability ratios, which fell significantly after the elemental diet. This change coincided with marked clinical improvement, as assessed by a disease activity index score.