Electro-oculographic, electromyographic and pathological findings in two cases of supranuclear lateral gaze palsy of pontine origin have allowed us to define the clinical and physiopathologic features of the Pontine Reticular Formation (PRF) syndrome, and to formulate hypothesis about the terminal portion of the Occipito-Pontine Tract (OPT) involved in horizontal pursuit eye movements. The unilateral PRF syndrome is characterized by abnormal eye movements in the direction of the lesion. In the ipsilateral hemifield of movement there is paralysis of all movements from midline to extreme ipsilateral side, except oculo-cephalic reflex which remains intact (dissociated palsy); in the contralateral hemifield all saccades from extreme contralateral side to midline are suppressed, and this constitutes a specific abnormality of the PRF syndrome: quick phase of optokinetic and vestibular nystagmus are absent, while voluntary gaze is preserved but remarkably slow. It is suggested that this last fact is due to simple disfacilitation arising from undamaged PRF. Electromyographic findings suggest that the division between excitatory and inhibitory fibers of descending supranuclear oculomotor tracts ending in the abducens nuclei probably occurs in the lower pans. Anatomopathologic findings in the two cases show that the OPT runs in front of the Medial Longitudinal Fasciculus or in the lateral tegmentum and that it decussates, at least once, below the upper pons.