Suction lesions of the left rostral superior colliculus (SC) and pretectal area were made in young rats. One to 50 days later, the right eye of each animal was injected with horseradish peroxidase (HRP). Animals were subsequently perfused and the brains processed with tetramethylbenzidine. In many older animals, lesioned areas were covered with thin membranes composed of glial and connective tissue cells. HRP-labelled optic axons were traced running through these membranes for up to 3 mm. On occassion, regrowing retinal fibres reached the rostral border of the remaining SC but did not grow into the tectal neuropil.