For the evaluation of postoperative upper gastrointestinal transit, the breath hydrogen test is a convenient method, which is simple but more reliable than the recording of clinical parameters such as bowel sounds. The test was used to study the effect of cisapride on the postoperative mouth-to-caecum transit time. Twenty patients undergoing cholecystectomy were tested pre-operatively and on the first postoperative day after having received either 10 mg of cisapride i.v. or matching placebo under double-blind conditions. The median preoperative transit time in the placebo group was 45 min, and the median postoperative transit time at least 3 h longer. The postoperative transit time after cisapride dosing was still longer than before the operation but was significantly (p = 0.02) reduced as compared with that after placebo administration.