The response to antidromic stimulation of the lateral geniculate body in cats is recorded as a triphasic wave, the first 2 deflections of which are identified, respectively, with the axon spike and the cell body spike. No electrical sign of dendritic activity was recorded. The cell body spike, in its brief duration and short refractory period, closely resembles the axon spike. Response of the geniculate neuron to synaptic stimulation was considerably longer than the cell body spike elicited by antidromic stimulation, and this is believed to reflect the ability of the neuron to resoond in different ways to substantially different types of stimulation. Slow negative and positive waves were found to signal, in an incomplete and unpredictable fashion, excitability changes in the neuron cell bodies. The positive wave was shown to indicate hyperpolarization of the cell body.