Explant culture of the adult goldfish retina results in vigorous neuritic growth, provided that the optic nerve has been previously crushed in vivo. The site of new membrane addition in these growing neurites was studied with a a membrane-binding lectin Concanavalin A (Con A) in conjunction with a fluorescent indirect antibody method. Explant cultures were labeled with Con A followed by rabbit antibodies to Con A. This treatment was shown to immobilize Con A receptors while permitting growth. Twenty-four hours later, the washed preparation was treated with fluorescent goat antirabbit antibodies. The bound fluorescent antibodies appeared as a pattern of contiguous fluorescent speckles confined to the area of old growth while regions near the distal end of the neurite were not fluorescent. These results are compatible with the hypothesis that new membrane is added in the region of the growing tip of the neurite.