Abstract:Healthy adult male frogs (Rana nigromaculata) were exposed to lead and cadmium to determine the ecotoxic- responses of MDA content and antioxidant enzyme (SOD, CAT, GSH-Px) activities in testes. The results showed: (1) The MDA content increased significantly with the increase of Pb or Cd concentration, displaying a clear concentration-effect relationship. The changes of the MDA content could show the injured degree in testes of Rana nigromaculata under a long-term exposure to Pb or Cd ; (2) The CAT and GSH-Px activities in testes increased significantly, whereas testicular SOD activity did not changes in all pb or Cd groups compared to control. The results indicated that GSH-Px and CAT activities played an important role in the prevention of oxidant damage in testes in response to the exposure of lead and cadmium; (3) In these three antioxidant enzymes, the GSH-Px activity was most sensitive, and the SOD activity was most insensitive to Pb or Cd exposure. Therefore, the change of GSH-Px activity in testes of the frog Rana nigromaculata is the best biomarker to indicate Pb or Cd exposure.