Gastrointestinal distress is commonly reported by athletes after ingestion of a beverage. We speculate that ingestion may be occurring after dehydration has taken place. The high prevalence of GI disorders in marathon runners who have lost ≥4% body weight supports this theory. To test this theory, the effects of dehydration, and dehydration in combination with endurance running, on gastric emptying (GE) and frequency of gastrointestinal (GI) complaints were tested in this experiment. A complete crossover study was designed. Sixteen subjects ingested 8 ml·kg BW−1 of a 7% carbohydrate (296 mOsm·kg−1), solution after a euhydration or dehydration regime. Dehydration (4% BW loss) was produced by 60% maximal speed running at 30°C or by intermittent sauna exposure at 100°C. Euhydration experiments were conducted with a 2 h rest period with water administered at 20 and 40 min. Gastric drink volumes were measured every 10 min for 40 min. Emptying curves were compared using semi-log transformation of the percentage emptying data and simple linear regression. The slope of each line was used as a measure of average GE rate. Dehydration-exercise resulted in slower GE than in all other treatments (P < 0.05). ANOVA revealed significant effects of dehydration (P < 0.05) and exercise (P < 0.05), these two effects being additive in delaying GE. GI complaints were reported by 37.5% of the subjects during dehydration-exercise experiments. No GI disturbance was reported in other tests. Core body temperature was significantly higher after the dehydration-exercise regime (39.1°C) than after the rest-dehydration regime (37.9°C) (P < 0.05). It is concluded that dehydration and/or thermal effects delay GE and may be related to a higher prevalence of GI disturbance.