Tilapia (Oreochromis niloticus) were exposed to 0, 100, 400, and 800 microg/g concentrations of Pb in diet for 60 days, and changes in growth performance, metabolic enzyme activities, and essential trace elements (Fe, Cu, and Zn) content in liver and kidney were investigated. Daily weight gain, feed conversation ratio, and survival of tilapia were not significantly affected by dietary Pb. Alanine transaminase (ALT), aspartate transaminase (AST), and lactate dehydrogenase (LDH) activities in liver and kidney were affected by dietary Pb in a dissimilar way: Pb concentration-related decreases in ALT, AST, and LDH activities were observed in kidney, while these enzyme activities in liver were stimulated in a Pb concentration-dependent manner. It was demonstrated that the inhibitory effects of dietary Pb on alkaline phosphatase, Na, K-adenosine triphosphatase (ATPase), Ca, and Mg-ATPase activities in both liver and kidney were Pb concentration-dependent. It was also indicated that the content of Fe, Cu, and Zn in liver and kidney decreased with the increasing dietary Pb concentrations. The results suggested that long-term dietary Pb exposure could affect metabolic enzyme activities and the content of Fe, Cu, and Zn in liver and kidney, whereas growth impairment was not observed in tilapia.