Studies of the reactions of neurones in the cochlear nuclei in the bat Myotis oxygnathus to ultrasonic stimulation show that 61% of the investigated neurones in a frequency range 20-40 kHz change tonic response for repetitive bursts, this change being dependent on the filling frequency and the intensity of stimulation. It is suggested that peculiarities of the neuronal activity result from the effect of a special inhibitory system presented in bats which uses in echolocation a wide range frequency-modulated impulses.