For the purpose of examining some of the principles underlying the function of primate visual cortex, the performance of one normal control group and three operated groups of Galagos having bilateral cortical lesions in area 17 (S), the middle temporal area (MT), or areas 18 and 19 (XS) was assessed on tasks measuring visual sensory capacity, search, and learning. Striate lesions produced a reduction in foveal vision and were responsible for deficits only on a complex visual learning task. The lesions of Group MT extended beyond area MT and involved the optic radiations. This resulted in impairments on all visual problems. Animals in Group XS had subtotal lesions of prestriate cortex and were also impaired on each task, but they showed less severe deficits in sensory capacity than animals in Group MT. It is suggested that the Galago's striate cortex plays a major role in the identification and utilization of relevant visual information and that areas 18 and 19 are important in both visual learning and visuospatial analyses. Evidence is provided that area MT is involved in visual search.