Intestinal inflammation may influence intraluminal pH. Profiles of the gastrointestinal pH were evaluated in 15 patients with active Crohn's disease of the ileocecal area. In addition, five patients with moderate (1) or severe (4) ulcerative colitis were studied. Fifteen healthy subjects served as controls. Intraluminal pH of the different parts of the gastrointestinal tract was measured by a free-floating pH-sensitive telemetering capsule. A metal sphere was attached to the capsule for exact localization by a metal detector. Physiological patterns of pH were maintained throughout the gastrointestinal tract including the inflamed segments. Median pH in the terminal ileum of the patients with Crohn's disease was 7.5 vs. 7.7 and in the rectum in ulcerative colitis 7.8 vs. 7.2 in the controls. In conclusion, intraluminal pH is not decreased by inflammatory changes in Crohn's disease and ulcerative colitis, allowing eudragit-coated pH-controlled-release formulations of mesalazine to dissolve in diseased areas also.