Primary cultures of rat oligodendrocytes were incubated with a fluorescent sphingolipid precursor, 6-[ N-(7-nitrobenz -2-oxa-l,3, -diazol-4-yl)amino] hexanoylceramide (C,-NBD-ceramide). This compound is known to stain the Golgi complex specifically. Within 30 min of incubation at 37Β°C most of the C,-NBD-ceramide was incorporated into the perinuclear Golgi system, as revealed by conventional and confocal laser fluorescence microscopy. Interestingly, c6-NBD-ceramide was found to accumulate also in smaller, oval-shaped structures in many of the processes, at distances up to 30 pm from the nucleus. This implies the possibility that these structures are Golgi (-derived) complexes. Indeed, after incubation of oligodendrocytes with C,-NBD-ceramide and rhodamine-labeled transferrin both fluorescent labels colocalized in the Golgi system of the cell body as well as in the structures in the processes. Additional support for the Golgi character of these structures was obtained by transmission electron microscopy. Particularly in oligodendrocytes cocultured with neurons, many Golgi structures were present all over the processes. The results lead us to conclude that, in the oligodendrocyte, the Golgi complex does not only reside in the perikaryon, but also in the processes. One can speculate that a polarized biosynthetic activity, involving the presence of the Golgi near the site of myelin synthesis, may be advantageous to the oligodendrocyte for assembly and/or repair of the myelin membrane at the distal end of the processes.