The role of the superior colliculus in the visual guidance of saccadic eye movements has been investigated. Rhesus monkeys are first trained and tested on several tasks which allow measurement and control of visual and oculomotor responses to stimuli in the central and peripheral visual field. After collection of normative data, the monkeys receive unilateral lesions of the superior colliculus. Following a period of postsurgical recovery without visual experience, monkeys are retested on the visuomotor tasks in order to assess the effect of the brain damage and to study the course of recovery. The monkey's postlesion ability to detect stimuli is impaired, but this recovers within several days of visual experience. The ability to make saccades to peripheral targets is permanently impaired as is optokinetic nystagmus. Pursuit eye movements remain normal.