Using a method of gradient gel electrophoresis coupled with autoradiography, we have analyzed the polypeptide composition of the proteins being transported down the axons of the projecting neurons of the rabbit retina. This analysis reveals: (1) the molecular weight distribution of 43 transported polypeptides; (2) the existence of at least four components of intra-axonal protein transport, each characterized by an unique polypeptide composition as well as by an unique velocity of transport; (3) the disappearance of individual labeled intra-axonally transported proteins from the axons and synaptic terminals with half-times ranging from several hours to more than 8 days. The possibility that intra-axonal transport functions as a temporal mediator of alterations in axonal or synaptic events is discussed in relation to these findings.