We evaluated colon manometry as a means of differentiating causes of intractable constipation in children. We studied pressure changes in the transverse, descending, and rectosigmoid colons of 23 children with intractable constipation. All patients had a history of less than one bowel movement per week for longer than 2 years without resolution after conventional medical management. The possibility of Hirschsprung disease was excluded in all. On the basis of pathologic and manometric studies of the upper gastrointestinal tract, 10 patients had a diagnosis of gastrointestinal neuropathy and two had a diagnosis of myopathy. The other 11 patients had functional fecal retention; this diagnosis was based on history and outcome of therapy. On the day of study we used endoscopy to place a manometry catheter into the transverse colon and recorded intraluminal pressure for longer than 4 hours. After obtaining a baseline recording, we gave the patient a meal to assess gastrocolonic response. Colonic contractions were recorded in 21 of 23 children. Children with functional fecal retention could be differentiated from those with neuropathy by examination of the postprandial record. After a meal children with functional fecal retention had (1) an increase in motility index (3.4 +/- 0.5 while fasting vs 9.1 +/- 1.3 postprandially; p less than 0.001), and (2) at least one high-amplitude propagated contraction (in 10 of 11 children). The patients with neuropathy had no high-amplitude propagated contractions (p less than 0.001 vs group with functional fecal retention) and motility index in these children did not increase significantly after a meal (2.7 +/- 1.0 while fasting vs 2.9 +/- 1.3 postprandially). The two children with hollow visceral myopathy had no contractions. We conclude that in children with severe chronic constipation the colonic results of manometry differentiate patients with functional fecal retention from those with neuropathy or myopathy of the colon.