Characteristics of single-unit activity in the superior olivary complex of Rhinolophus ferrum-equinum in response to ultrasonic stimuli with a pulse frequency within the echolocation range were studied. Some neurons were found to have three separate response areas with characteristic frequencies corresponding to one half and one third of the basic frequency ranging from 80 to 86 kHz. When the intensity of stimulus with a pulse frequency equal to the characteristic neuron frequency increased, the tonic response changed into phasic activity. With the use of two overlapping stimuli a change from phasic to tonic response occurred. The frequency of tonic discharge corresponded precisely to that of beats up to 2000 Hz (synchronism of neuronal discharges with each beat cycle). Synchtonized tonic activity persisted under specific pulse frequencies and stimulus intensities.