The effect of the heavy metals Cu, Zn, Cd and Pb on the gill and liver tissues of the Nile tilapia, Oreochromis niloticus was examined in the laboratory. One hundred and fifty adult fish were divided into five groups (control, copper, zinc, cadmium and lead) each group containing 30 fish. They were continuously exposed to sub- lethal concentration of each metal (lmg/L) for a period of 10 days. From each group, the gills and liver of six fish were removed after 10 days and the remaining fish were transferred to tap water for:a recovery period (21days). The tissue samples of gills and liver of both treated and recovery fish were dissected for histological examination. The results showed that the extent of distortion of the gills and liver was more pronounced in the fish group that were exposed to Cd&Pb.