AbstractThe transport of RNA from the ganglion cell bodies within the retina to the contralateral optic tectum has been studied in the chick following intraocular injection of radioactive uridine. By tracing the appearance of labeled RNA at the proximal end of the optic nerve as it leaves the eyeball and comparing this to the time of arrival of RNA within the optic tectum, the migratory velocity of axonal RNA has been calculated to be around 12 mm per day. The continuation of RNA migration to the optic tectum in the presence of intracerebrally injected actinomycin‐D but not in the presence of the intraocularly injected drug, suggests a retinal site of synthesis of the excess RNA found in the tectum innervated by the injected eye. A study of the rate of disppearance of radioactivity of the transported RNA in the optic lobes, suggested that this RNA turns over more rapidly than the bulk of tectal RNA. The destination of migrating RNA within the optic tectum has been autoradiographically examined. Most radioactive RNA is found in the outer tectal layers in which are found the afferent fibers of the optic tract and most of their synaptic terminations. Label is not confined to these areas however but is also present in the deeper layers of the optic tectum which are not known to contain any primary synapses of the axons from retinal ganglion cells.