This study investigated the effects of arginine supplementation on acute metabolic responses during recovery after a single bout of endurance exercise in trained athletes. Twelve healthy male judo athletes were randomly divided into two groups and performed a single bout of exercise at a speed estimated to correspond to 75% VO2max for 60 min, and then took either a placebo or arginine at 0.1g/kg-wt. Blood samples of each athlete were collected before exercise, and 0, 15, 30, 45, 60, 90, 120 min after exercise, respectively. The experiment was repeated two weeks later, but treatments were exchanged for the two groups. The concentrations of glucose, insulin, free fatty acid (FFA), glycerol, lactate, ammonia, creatine kinase, and NO(subscript x) (NO2(superscript -)+(NO3(superscript -) in blood were examined. No differences in the levels of glycerol, lactate, ammonia, creatine kinase, or NO(subscript x) between the two groups were observed at any of the time points. However, the concentration of glucose was significantly higher in the arginine group as compared to that in the placebo group at the 15-min recovery point. The insulin concentration was also higher in the arginine group as compared to that in the placebo group at the 30-min recovery point. Furthermore, the free fatty acid levels at the 30, and 45-min recovery points were significantly lower in the arginine group compared to those in the placebo group. The results indicated that arginine supplementation during the exercise recovery period could increase glucose and insulin concentrations, and decrease FFA availability in the blood.