Single-unit firing patterns of neurons in the medial geniculate body were studied in response to 0.1 msec, clicks in cats which were either lightly anesthetised with barbiturates or unanesthetised and paralysed with gallamine. Unit responses were analysed with a modified multichannel scaler which derived the averaged response histogram and interval histogram for each unit studied, Three main types of averaged response pattern were observed. One type of unit responded to a click by evoking a spike or group of spikes at short latency (8-16 msec). The other types of unit fired spontaneously, the spike activity of the 2nd group being suppressed for 40- 200 msec, following click presentation whilst units in the 3rd group exhibited reverberating responses in which periods of excitation and inhibition alternated in a regular way. The 3 types of response pattern were quantitatively, but not qualitatively, affected by the presence of an anesthetic agent. The 3 types of unitary response pattern could also occur in the absence of the homolateral cortical auditory areas.