Physical exercise has influence on all organs except its effects oil the central nervous system have not been fully elucidated. This study attempts to determine whether the degree of training could affect the response to physical stress by comparing the three groups of males in different levels of the physical fitness. Serum samples from high (n = 11), moderate (n = 10), and low physical activity sportsmen (n = 10) were collected to determine nitrite/nitrate levels before and after carrying out an anaerobic maximal exercise test. All "oddball paradigm" of auditory stimuli was used to evoke the N200 and P300 before and after the exercise. The amplitude of the N200 decreased significantly after anaerobic maximal exercise compared to the values of the recorded pre-exercise at Fz area in high physical activity group. There was a negative correlation between event-related potentials component and both nitrite/mtrate serum level changes and the heart rate changes in low physical activity subjects. However. in high and moderate physical activity groups, these relationships were positive.