Experiments were performed in unanesthetized awake monkeys to determine the effects of cerebellar stimulation on the activity of single cells within a chronic alumina cream seizure focus in the motor cortex. Six indices were used to characterize the epileptic and non-epileptic activity of the neurons within the focus. Cerebellar stimulation did not produce any statistically significant effect on these indices. This was partly due to large fluctuations in these parameters which occurred independent of the stimulus. Therefore it was concluded that these negative results were due to the intrinsic variability in these parameters and that an evaluation of cerebellar stimulation based on these indices was not adequate. Therefore, cross-correlation analysis was used to examine the effects of cerebellar stimulation on the excitability of neurons within the focus. This technique demonstrated that cerebellar stimulation modulated neuronal activity in the focus with 3 different profiles. These alterations in excitability were similar during the occurrence of either epileptic or non-epileptic activity in a single neuron. These results show that cerebellar stimulation can increase and decrease the excitability of neurons in an experimental seizure focus during both epileptic and non-epileptic activity.