1. The auditory threshold curve of averaged evoked potentials of the colliculus inferior in Rhinolophus /errum equinum to pure tone stimulation from 1 to 100 kHz is presented (Fig. 1). For pure tone frequencies lower than 14 ktIz thresholds steeply rise from 20 to 110 db. The steepness of the acoustical filter for 83.3 kHz signals and the frequency of the echoes heard by Greater Horseshoe Bats is accentuated by averaging methods. Because of averaging, evoked potentials thresholds are lowered by about 20 db compared to those obtained by non-averaging methods. 2. Prominent off-responses in evoked potentials appear for three stimulus frequency ranges: 3-10 kHz with a peak at 5 ktIz, 20-40 kHz with a peak at 20 kHz and 80.0-82.6 kHz with a peak at 81.5 kHz (Fig. 2). 3. It is unlikely that beat note frequencies play any role for echolocation. 4. The relevance of these results to echolocation in Horseshoe Bats is discussed, especially as to Doppler shift information contained in the constant frequency part of echoes.