&NA;The sensitivity of large intestinal absorption topH and the absorption of short‐chain fatty acids were measured in ulcerative proctocolitis by a dialysis bag method. Lowering luminalpH from 7 to 5.5 significantly reduced absorption of salt and water in proctocolitis, but not in normal controls. Short‐chain fatty acid absorption was not affected by inflammation or change inpH when patients with ulcerative proctocolitis were compared with controls.