Extracellular activity of 124 caudate nucleus neurons during stimulation of parvo- and magnocellular parts of the medial geniculate body by rectangular electrical stimuli were investigated in chronic experiments on cats. Reactions were observed in 54 neurons (43%). Main types of responses were: phasic activation in the form of a single spike or spike discharge, initial activation followed by inhibition and pure inhibition. Excitatory responses prevailed (81% of the reacting neurons). The latent periods in different units fluctuated from 2.7 to 64 ms. In the same unit the latent periods were also very variable, which permits considering them as orthodromic. The mode of the histogram of the latent periods of the excitatory responses was in the range of 9-12 ms. The latent periods of the inhibitory responses varied from 12 to 130 ms and were in most neurons in a range of 40-60 ms. The increase in stimulus intensity led to an increase in response regularity, an increase in the number of spikes, reduced latent periods. In the same neuron the character and the structure of responses to stimulation of the relay nucleus and to sound clicks were usually identical. The latent period of responses to clicks was larger. Peculiarities of functional connection of the medial geniculate body with the caudate nucleus as a forebrain polymodal unspecific structure are discussed.