Between 30 - 50% of patients undergoing surgery suffer from post-operative nausea and vomiting which may be associated with pulmonary aspiration, and fluid and electrolyte imbalance. This thesis has explored the upper gastrointestinal motor associated with nausea and vomiting in peri-operative patients. Specific objectives were: 1. Evaluation of motor disturbances in the upper gastrointestinal tract associated with emesis in the first 24 hours following surgery; 2. Development of a novel computerised method for recognition and measurement motor abnormalities associated with emesis; 3. Investigation of intragastric pH changes associated with bile shifts and bile vomiting; 4. Evaluation of the effects of specific antiemetic therapy and laparoscopic surgery on upper gastrointestinal dysmotility following cholecystectomy; and 5. Investigation of the contribution of opiate analgesia to symptoms and motor disturbances associated with post-operative vomiting. In a human model of emesis, we have shown the presence of small bowel phasic bursts which migrate in a retrograde fashion. These retrograde phasic bursts are significantly associated with vomiting episodes. Such motor abnormalities can be measured by a novel computer programme during prolonged ambulatory recordings. During the post-operative period gastric pH rises, possibly as a consequence of enterogastric flow of bile and subsequently falls when vomiting occurs. The potent 5HT3 receptor antagonist antiemetic, ondansetron, ameliorates post-operative nausea and vomiting symptoms and is associated with a reduction in retrograde activity in the small bowel. Morphine, when given to healthy volunteers, induced similar motor patterns to those observed during post-operative emesis. Emesis in volunteers was also associated with retrograde small bowel phasic activity. This motor response to opiates may contribute to post-operative nausea and vomiting.