5′-Nucleotidase, a prominent nucleoside-producing ectoenzyme of glial plasma membranes, was studied by enzyme cytochemistry in the superior cervical ganglion of the rat under normal conditions and after pre- and postganglionic axotomy. In normal ganglia 5′-nucleotidase was restricted to capillary endothelial cells, localized both on the luminal surface and in pinocytotic vesicles. Following preganglionic axotomy, the number of enzyme-positive endothelial vesicles increased, whereas no 5′-nucleotidase was found on reactive Schwann cells during phagocytosis of degenerating preganglionic axon terminals. After postganglionic axotomy an even stronger increase in enzyme-containing endothelial vesicles occurred. In addition, 5′-nucleotidase activity became detectable on the plasma membrane of Schwann cells and proliferating satellite cells, which participate in the detachment of synapses from axotomized neurons. Fibroblasts in the endoneuronal connective tissue of regenerating ganglia also exhibited 5′-nucleotidase on their surface. The results obtained suggest that 5′-nucleotidase may be related to specific metabolic requirements of Schwann and satellite cells during regeneration and that these requirements differ from those of reactive Schwann cells after denervation of the ganglion. Postoperative changes in 5′-nucleotidase activity on endothelial cells and fibroblasts of the ganglion indicate an involvement of these cells in metabolic response elicited by pre- or postganglionic axotomy.