Single units were recorded from the inferior colliculus (IC) of anaesthetized rats in response to: (a) an FM tone, the frequency of which was randomly varied, and (b) a digitized rat vocalization sound. We hypothesized that these neurons may have 'orientation-specific' spectrotemporal receptive field (STRF) that can be used to estimate their responses to complex communication signals. Based on the FM response, we first estimated the cell's STRF which was then convolved with the spectrogram of the rat's vocalization call. A simple convolution gave only crude prediction of the cell's response to the vocalization sound. When inhibitory areas were added around certain parts of the STRF, a better match was found. We conclude that for some FM-sensitive neurons of the IC, STRF with inhibitory areas may account for their responses to vocalization sounds.