Effect of diet in general, and glycogen storage in particular on the performance ability of athletes has been well documented. In this study, an effort was directed to further clarify the effect of the body glycogen storage on the blood glucose level and the running record in the long distance runners. Forty-two male high school athletic students of 15 ~19 years of age who are well trained as the long distance runners were selected. The subjects were divided into three groups: i.e, the control, low carbohydrate (LCHO) and high carbohydrate- (HCHO) group. HCHO group was supplied with a high fat and high protein diet for two days with a hard running exercise followed by a high carbohydrate diet for 3 days with a light running erercise. LCHO group received a high fat and high protein diet with a hard running exercise. A long distance running of 1) 20km at a full speed and 2) 10km at a constant speed of 18km per hour was performed. LCHO group performed only 10km running. The blood glucose concentration was determined by an enzymatic method, venous blood pH by using the Corning model 175 automatic blood gas analyzer, blood lactate concentration by the method of Barker and Summerson, heart rate by palpating the radial artery. The following results were obtained. 1. Blood glucose concentration: After 10km running, both the control and HCHO groups showed increased values in comparison to the resting values immediately and 10 min after exercise, while LCHO group showed lower values than the resting values immediately, 10 and 30 min after exercise. The LCHO group showed values than the control group immediately and 10 min after exercise. After 20km running, the control group showed increased values compared with the resting values during exercise (10km point) but showed decreased values in comparison to the resting values immediately after exercise. The HCHO group showed increased values in comparison to the resting values immediately, 10 and 30 min after exercise. The HCHO group showed higher values than the control group immediately and 10 min. after exercise and the difference was especially remarkable immediately after exercise. 2. Blood lactate concentration: After 10kra running, all 3 groups showed increased values compared with the resting values where the LCHO group showed lower values than the control group immediately, 10 and 30 min. After 20km running, both the control and HCHO groups showed increased values comparision to the resting values, where the HCHO showed higher vahaes than control. 3. pH of -venous blood: Both the control and HCHO groups showed decreased values in comparison to the resting values during and immediately rafter exercise. The HCHO group showed lower values than control group immediately after exercise. 4. Heart irate: After 20km running, both the control and HCHO groups showed increased values compared with the resting values, where HCHO group showed lower values than, the control group immediately, 3 and 5 min after exercise. 5. Record: The HCHO group showed shorter values than die control group after 20km running at a full speed. From the above results, we could note that blood glucose level was increased due to the increase of glycogen storage in the body and that subsequently the subjects made a shorter record through the dietary regime.