Orocoecal transit time (OCTT), assessed by means of H2 breath test after lactulose and/or after a semisolid standard meal, was studied in normal and constipated children. Both control subjects and patients with constipation showed a significantly longer OCTT after a standard meal than after lactulose ingestion (p less than 0.01). Whereas the OCTT after lactulose did not differ in the two groups, the constipated patients had a significantly longer transit time after a standard meal when compared to controls (p less than 0.05). No correlation was observed within each group between the OCTT after a standard meal or after lactulose ingestion (r = -0.077; p greater than 0.01). These findings suggest that 1) measurement of the transit of a standard meal instead of a lactulose solution may offer more direct insight into the role of small intestinal transit of food, both in physiological and pathological conditions, 2) gastrointestinal segments other than colon may play a role in chronic non organic constipation of childhood.