A group of 55 patients with homonymous field defects related to vascular or traumatic postgeniculate damage were trained by locating light targets presented within their blind field region. This systematic treatment led, in the majority of patients, to an enlargement of the visual field. Recovery depended on specific practice. Control experiments showed that field enlargement cannot be explained by eccentric fixation or perimetric measurement variability. It is hypothesized that recovery may take place at striate cortex level and may result from 'reactivation' of reversibly damaged nervous tissue. In cases that did not benefit from treatment, visual field loss may result from irreversible damage.