Background: IL-8 is a chemokine which recruits endothelial progenitor cells and induces angiogenesis. In the present study, we examined whether exercise could increase serum level of IL-8 and compared the response in obese and non-obese subjects. Methods and Results: Fifteen non-obese (BMI<25 kg/m2) active healthy volunteers and sixteen obese (BMI>25) sedentary volunteers participated in this study with informed consent. All were men and 20 years old. Mean body mass index was 24.1짹1.1 (non-obese group) and 27.7짹0.8 (obese group), respectively. In addition, body fat mass was calculated by body composition analyzer. We measured serum levels of IL-8 and VEGF at rest using ELISA before and 5 weeks after daily strenuous exercise. Before exercise, there was no significant difference between the groups (p=0.19 for IL-8 and p=0.096 for VEGF). After 5-week exercise, BMI of obese group was markedly decreased (p<0.001) whereas that of non-obese group was not changed (p=0.06). The level of IL-8 was significantly increased in the obese group (p=0.001) whereas it was not in the non-obese group (p=0.23). The level of VEGF, however, showed no difference after exercise. The change of IL-8 was correlated with that of body fat mass (Spearman���s coefficient = -0.45, p=0.018). Conclusion: IL-8 was significantly increased by exercise in obese individuals whereas VEGF was not changed in both groups. Therefore, IL-8 may be an important exercise-induced cytokine which provokes angiogenesis and thus improves tissue perfusion and metabolism.