The bipolar surface electromyogram (EMG) of the biceps brachii of school children was recorded during isometric contraction. The EMG power spectrum was obtained for the frequeny range from 6Hz to 192Hz by the autocorrelation and its Fourier transformation technique. The EMG power spectra of school children were compared with those of male adults examined previously. There was no significant difference in the EMG power spectra between school boys and school girls, and between school children and male adults. It could be concluded that the power spectra of the surface EMG are not affected by age and sex in healty subjects aged at least between 5 and 25 years.