Aim of this research was to investigate the effects of acute, mid-line and symmetrical split carried out at different levels of the brain on the ocular nystagmus brought about in the guinea pig by low-frequency electrical stimulation of the temporo-parietal cortex or of the nystagmogenic fibers running in the superior colliculus and by thermal stimulation of the labyrinth. Mid-line split: i) of the corpus callosum and of diencephalon, ii) of the mesencephalon and iii) of the most rostral part of the bulb, just caudal to the nuclei of the VIth cranial nerve, did not abolish the eye nystagmus. However, this was suppressed by split of the pons at the level of the abducent nerve nuclei or just rostral to this formation. Under such experimental conditions the labyrinthine and the central stimulations could elicit only occasionally a slow eye deviation.