The effects of ingestion of fructose (F), as well as of arginine (A) and citric acid (C) on both carbohydrate metabolism and lipid metabolism during prolonged exercise in seven distance runners on treadmill running were investigated by comparing it with those of glucose + arginine + citric acid (GAC) and placebo. With the values of the plasma glucose, though FAC as well as placebo contrastively indicated almost a flat distribution, GAC increased from 30 min rest before the exercise (i.e., the time for 500 ml intake of GAC) to the beginning of the exercise. The plasma glucose for GAC showed significantly higher values (138 +/- 22 mg/dl) than that for FAC or placebo, whose values were 102 +/- 18 mg/dl and 93 +/- 8 mg/dl, respectively. The plasma glucose for GAC was likely to decrease gradually as the exercise progressed more. At the end of exercise, however, the plasma glucose for FAC indicated significantly higher values (100 +/- 12 mg/dl) than that for GAC, whose values were 89 +/- 12 mg/dl. Though the serum free fatty acid showed upward tendencies of values in all cases of FAC, placebo, and GAC as the exercise progressed, no significant difference of the values in those cases was observed (the following values were drawn at the end of the exercise; FAC:655 +/- 185 microEq/l, placebo:603 +/- 289 microEq/l, GAC:485 +/- 140 microEq/l).(ABSTRACT TRUNCATED AT 250 WORDS)