Summary Postoperative intolerance of oral fluids is common after abdominal surgery, and their premature administration may result in abdominal distension, nausea and vomiting. The ability of the stomach to empty 100 ml of water was investigated in patients undergoing elective cholecystectomy. Patients were studied preoperatively and on the first postoperative day using a radio-isotopic method of measurement of gastric emptying. Factors such as age, electrolyte disturbance, duration of operation and the many drugs used during the perioperative period were analysed in relation to postoperative gastric emptying rates. Postoperative gastric emptying showed wide variation, being normal in some patients but absent in others. No correlation was found between postoperative gastric emptying and age, plasma potassium and the duration of operation and anaesthetic. A significant correlation was found, however, between gastric emptying and drugs administered in the perioperative period. In particular, gastric emptying was grossly retarded following an injection of opiate, but this returned to normal if more than 5 h had elapsed since the last injection of opiate. It is suggested that opiate therapy is a major factor in a patient's inability to tolerate fluids following cholecystectomy.