Objectives: We sought to evaluate colonic gas accommodation, ileocecal competence, and colonic clearance in subgroups patients with abdominal bloating.Methods: Thirty-six patients complaining of abdominal bloating (12 constipation-predominant irritable bowel syndrome (IBS-C), 12 diarrhea-predominant irritable bowel syndrome (IBS-D), and 12 functional bloating) and 18 healthy controls were studied. Abdominal perception and girth were measured during: (i) 1 h continuous infusion of gas at 24 ml/min into the rectum (accommodation period) and (ii) 30 min free rectal gas evacuation (clearance period). In eight patients and eight healthy subjects, the gas infused was labeled with radioactive xenon (74 MBq 133 Xe), and gas distribution was determined by scintigraphy.Results: Colonic gas accommodation produced significantly more abdominal symptoms and distension in patients than in healthy subjects (3.8±0.2 vs. 2.4±0.3 perception score; P<0.001; 10.90.6 vs. 8.30.5 mm girth increment; P=0.009). Scintigraphy showed no differences in colonic gas distribution and no ileal gas reflux, but patients exhibited impaired gas clearance from the proximal colon (63%10% clearance in 30 min vs. 80%2% in health; P=0.042), resulting in more residual gas (506±46 vs. 174±47 ml; P<0.001), perception (1.9±0.2 vs. 1.0±0.2 score; P<0.015), and girth increment (4.2±0.7 vs. 2.2±0.5 mm; P<0.024); IBS-C patients exhibited increased sensation and objective distension, as opposed to sensation only in IBS-D and distension only in functional bloating.Conclusions: Patients with abdominal bloating have normal colonic accommodation and ileocecal competence but impaired gas clearance from the proximal colon after retrograde infusion, and the consequences of this dysfunction are related to bowel habit. © 2010 by the American College of Gastroenterology.