The auditory cortes of cats immobilized with d-tubocurarine was stimulated by monopolar macroelectrodes (tip diameter 100 mu) or micloelectrodes (tip diameter 100--15 mu). In both cases in cortical neurons located closely to the stimulation point IPSPs were recorded with latencies ranging between 0.4--1.2 and 1.4 6.0 ms. It is suggested that IPSPs of the first group are generated in response to direct stimulation of the bodies and axons of the inhibitory cortical neurons (monosynaptically). The amplitude of such IPSPs ranged in different neurons from 3 to 15 mV and their duration was between 4 and 15 ms. Many of them were complicated by later additional inhibitory volleys. 1.5% of all IPSPs generated in response to geniculocortical fibres stimulation had latencies between 0.8--1.3 ms. It is suggested that these IPSPs were also evoked monosynaptically.