This investigation is mainly concerned with the histopathological effects of the metacercaria of the parastiic trematode Euclinos tomum ardeolae (EL-NAFFAR and KHALIFA, in press) on the kidney of the Nile cichlid fish Tilapia nilotica. Fifteen fishes, including normal, slightly infected and haevily infected ones were investigated. The glomeruli, proximal and distal convoluted tubules, collecting tubules and intertubular connective tissue displayed clear signs of degeneration, the extent of which depends on the intensity of infection.