ABSTRACTSeveral experiments have shown that monocular occlusion (MO) leads to a variety of changes in the visual functioning of the non-occluded eye. An experiment was conducted to assess the effect of 24 hr of MO on the lateral phoria, a binocular phenomenon. The results demonstrated marked tendencies for increased esophoria after MO, especially for near vision. Follow-up tests revealed that normal phoria was reestablished 24 hr after the termination of MO. The results are discussed in the context of the use of MO in treatment procedures for visual dysfunctions and their implication for future investigations.