In this study, levels of reduced glutathione (GSH) and metallothionein (MT) which are known to be biomarker of metal exposures were measured in a freshwater fish Oreochroinis niloticus following exposure to 0, 5, 10 and 20 mu M concentrations of Cu, Zn, Cd and Ph for 14 days. Metals and GSH were measured in the liver, gill, intestine, muscle and blood, and MT in the liver. Copper accumulation occurred only in the gill, while Zn accumulation occurred only in the muscle. Lead accumulated in the liver and gill, whereas Cd accumulated in all the tissues. Metal exposures did not alter GSH levels in the blood, muscle and gill, but its levels increased in the liver following Cd, Zn and Cu exposures. NIT levels in the liver increased only in Cd-exposed fish. The results showed that there was no significant change in tissue GSH levels following metal exposures, except in the liver. The levels of liver GSH increased significantly by all the metals, except lead. Data indicated that only the liver may be suitable indicator tissue to determine the response of GSH and MTs to metal exposure in environmental monitoring studies. (c) 2007 Elsevier B.V. All rights reserved.