Summary—The glucose‐6‐phosphatase (G6Pase) activity of cytoplasmic components of spermatocytes and spermatids of the rat was examined by electron microscope cytochemistry using cerium chloride as a capture agent. G6Pase activity, a recognized ER‐resident enzyme, was present in all ER cisternae of spermatocytes. In spermatids, while some ER cisternae were G6Pase‐reactive, others were negative or only slightly reactive, indicating an unequal distribution of the enzymatic activity throughout the network of ER cisternae in these cells. In spermatocytes, thecis‐ andtrans‐elements of the stacks of Golgi saccules were slightly but significantly reactive for G6Pase. In the Golgi apparatus of spermatids, thecis‐element, 4 or 5 underlying saccules, as well as one or two thicktransGolgi elements were G6Pase reactive. The G6Pase activity of the various Golgi elements, like that of the ER cisternae was not affected by the pH of the medium and was completely inhibited by Na‐vanadate, a known G6Pase inhibitor. Sertoli and Leydig cells, submitted to the same cytochemical conditions, showed complete G6Pase reactivity of their ER; however in Sertoli cells, all Golgi components were consistently negative while in Leydig cells thecis‐ andtrans‐elements of the Golgi stacks were slightly reactive, as in spermatocytes. Thus, the G6Pase reactivity of Golgi elements, appeared variable from one cell type to another. The compact juxtanuclear Golgi apparatuses of spermatocytes and spermatids were both associated with numerous G6Pase reactive ER cisternae; some were present at their surface, others crossed their cortices between Golgi stacks and formed elaborate networks in their cores. Other ER cisternae, in turn were closely apposed to or intertwined withtrans‐elements of the Golgi stacks, a relationship raising the possibility of molecular exchanges at this pole of the s