The effects of zinc and copper salts on the survival of the two species of freshwater fish, common carp,- Cyprinus carpio, and grass carp, Ctenopharyngodon idellus, were investigated. It was discovered that the levels of tolerance to the concentration of the metals were species-specific. Cyprinus carpio was found to be more susceptible to copper, whereas Ctenopharyngodon idellus was more susceptible to zinc. In general, copper was more toxic than zinc, as revealed by the survival times. The body and the gills of dead fish seemed to be covered by a veil-like film which looked like coagulated mucus and which was formed by the heavy-metal ions reacting with some constituents of the mucus secreted by the gill. The histopathological assessment of the gill and liver of Cyprinus carpio was also carried out. Particles were observed around the gills of the dead fish treated with zinc and copper salts, although no other major changes were found in the gill. Several histopathological changes were observed in the livers, including the presence of particles. The symptoms of the liver suggested that the internal injury was also an important feature of the intoxicants.