AbstractIn order to analyse, at the electron microscope level, the three‐dimensional configuration of the trans compartment of the Golgi apparatus rat dorsal root ganglia were treated to demonstrate cytidine monophosphatase (CMPase) activity. The localization of enzymatic activity in the Golgi apparatus varied according to cell types. In type A and C cell, CMPase was exclusively located in the transmost sacculotubular element, whereas in type B cells all the saccules of the stacks forming the Golgi ribbon and the trans‐Golgi networks were impregnated. Numerous dense bodies seen at proximity were also CMPase positive. In 3 μm thick sections of type A cells examined at low magnification, the impregnated element was scattered throughout the cytoplasm and never formed a continuous structure. In type B cells, the strongly reactive trans‐Golgi networks did not follow the entire length of the impregnated Golgi ribbon but were preferentially located in the concavity of its arched portions. At higher magnification and in all cell types some tubular portions of the trans‐Golgi networks took the apperance of spheroidal cage‐like structures, the CMPase positive anastomotic tubules forming the bars of the cage. Anastomotic tubules separated from the trans‐Golgi networks formed fenestrated spheres, while nearby CMPase‐reactive dense bodies exhibited a paler hilus. These observations were taken to indicate that in ganglion cells, some CMPase positive dense bodies, presumably lysosomes, formed by fragmentation of the trans