Synaptic glycoproteins are synthesized and glycosylated in the neuronal cell body, and conveyed to terminals by fast axonal transport. We used the α‐mannosidase inhibitor, 2‐deoxyman‐nojirimycin (dMan), to investigate the effects of disrupting N‐glycan processing on the axonal trafficking of proteins in vivo. dMan significantly reduced rapid axonal transport in retinal ganglion cells to about 34% of control values 4 h after metabolic labeling; at 8 h post‐labeling the inhibition was reversed. 2‐D gel analysis showed that dMan completely inhibited the arrival of radiolabeled L1 and NCAM at axon terminals, and resulted in the appearance of two novel proteins of 230 kDa and 155 kDa. Our results show that disruption of the N‐glycosylation pathway has an immediate inhibitory effect on total axonal transport and longer lasting effects on the trafficking of specific glycoproteins to axon terminals in vivo.