Approximately 50% of athletes will develop gastrointestinal symptoms at some stage in their careers. These range in severity from heartburn to gastro-intestinal bleeding. Fortunately symptoms are usually mild and inconvenient, but in certain individuals they can be incapacitating. It is important to exclude the more common gastro-intestinal conditions before diagnosing exercise-related syndromes. However, once such a diagnosis has been made, therapeutic options are limited. The physiological role of the gastro-intestinal tract in fluid and energy replacement is increasingly being recognised. Without adequate replacements, performance may be limited. The volume of fluid ingested during endurance events needs to be limited to actual requirements; 500 ml/h is the average. Greater volume intake may be associated with overhydration and hyponatraemia. Glucose supplementation is essential for adequate performance in events of 2-3 hours' duration or longer. Studies of hyperosmolar carbohydrate solutions and their influence on energy and fluid emptying from the stomach suggest that higher carbohydrate concentration solutions than those often used by athletes may be advantageous.