To determine the effect of a carbohydrate-(CHO) enriched diet on long-term, intermittent exercise performance, seven professional soccer players (mean maximum oxygen uptake: 60.6 (range: 56.0-65.1) ml.min-1.kg-1) were tested twice. The standardized test consisted initially of a field part (6856 m) followed by treadmill running to exhaustion. The relative work rates were 65, 57 and 81% of maximum oxygen uptake during the field test, and during the first and last part of the treadmill running, respectively. The players ingested a diet containing either 39% (C-diet) or 65% carbohydrate (CHO-diet) during the two days prior to each test. The order of the diets was assigned randomly. Neither blood lactate nor glucose concentrations at exhaustion differed after the two diets. The total mean running distance after the CHO-diet was 17.1 km, which was 0.9 km longer (p less than 0.05) than after the C-diet. Nevertheless, three subjects had a difference in running distance of less than 420 m. In contrast to the remaining players, these players had a higher RER-value during treadmill running in association with the CHO-diet. The mean CHO intake of 46% in the normal diet of the players was below the Nordic Nutritional Recommendation. In conclusion, performance during intermittent running was enhanced following the ingestion of a CHO enriched diet for two days. However, not all players benefited from the CHO-diet perhaps because they, in contrast to the other players, responded with a higher utilization of CHO after the CHO-diet.