Single-unit extracellular recordings were made in the lateral (LTN) and dorsal (DTN) terminal nuclei of the accessory optic system (AOS) of 10 monocularly deprived cats. The separate effects of monocular deprivation (MD) observed in each hemisphere are outlined below. Unlike many units in normal animals, LTN and DTN cells in the hemisphere contralateral to the non-deprived (open) eye, were no longer activated through visual stimulation of the ipsilateral (deprived) eye. In both nuclei, cells were driven effectively only by stimuli presented via the contralateral eye. The distribution of preferred directions was considerably altered in the LTN but not in the DTN. Almost every LTN unit encountered in MD cats preferred downward stimulus motion, in contrast to normal animals where equal numbers of LTN cells show preferences for upward and downward movement (J. Neurophysiol., 51 (1984) 276-293). DTN units showed the usual preference for horizontal motion toward the recorded hemisphere. Velocity preferences were slower on average in the DTN, and unaffected in the LTN. In the hemisphere contralateral to the deprived eye, the ocular dominance distribution of LTN and DTN cells showed a distinct shift in favor of the contralateral (deprived) eye. This effect was not as complete as that observed in the other hemisphere. Cells in both nuclei displayed a small influence from the ipsilateral (exposed) eye in some animals, but this input was much less than that observed in normally reared cats. Average velocity preferences among DTN units were slower than normal, and slower relative to the DTN population in the opposite hemisphere. No pronounced changes were observed in LTN velocity tuning. The distributions of preferred directions for both nuclei were similar to those obtained in the other hemisphere: DTN cells were found to prefer horizontal motion, while most LTN units were activated best by stimuli moving vertically and down within their receptive fields.