Histochemistry for nucleoside diphosphatase was used to study the microglial cells in the adult tench retina. An abundant population of microglial cells was located in the vascular membrane, nerve fibre layer, inner and outer plexiform layers and scattered cells were observed in the inner nuclear layer. Rounded and amoeboid cells could be seen close to the vessel in the vascular membrane, bipolar cells in the nerve fibre layer and ramified cells in the rest of the layers. Several microglial forms could correspond to developing cells. The pattern of distribution was similar to that described in other vertebrates, but with several differences, such as the presence of microglial cells in the vascular membrane and inner nuclear layer and the overlap of processes in the plexiform layers.