Electrophysiologic effects of physical exercise were investigated by comparing groups of individuals who engage in regular intensive physical exercise (12 + h/week) to control subjects (2 + h/week). Electroencephalographic (EEG) activity was recorded under eyes open/closed conditions to assess baseline differences between these groups. Spectral power was less for the exercise compared to the control group in the delta band, but greater in all other bands. Mean band frequency was higher for the exercise compared to controls in the delta, theta, and beta bands. Some differences in scalp distribution for power and frequency between the exercise and control groups also were found. The findings suggest that physical exercise substantially affects resting EEG. Theoretical mechanisms for these effects are discussed.