We reported the detection of high-frequency variations in the hydrogen Balmer lines in the hot star [eta] UMa of spectral class B3V. Spectral observations of [eta] UMa were carried out with slitless spectrograph (R~100) installed on the 60 cm Carl Zeisstelescope in the Andrushivka Observatory. Spectra were obtained with a time resolution in the sub-second range. It has been found that the [eta] UMa shows rapid variations in the hydrogen lines H[alpha], H[beta], H[gamma], as well as variations in the atmospheric oxygen lines. The intensity variations in the hydrogen lines varies from 0.2% to 0.5%, and that of the oxygen lines is approximately 2%.
