In this study, the effects of heavy metals (Cd, Cu, Pb, Zn) on EROD and CYP3A4 activities in the earthworm Eisenia fetida were evaluated to find out their possible induction and potential as biomarkers for soil heavy metal contamination. The earthworms were exposed to increasing concentrations of Cd (0.1-8 mg L-1), Cu (10-200 mg L-1), Pb (20-400 mg L-1) or Zn (50-400 mg L-1) in filter papers for 48 h. EROD activity was significantly changed in dose-dependent manners after exposure to each of the four metals. CYP3A4 activity was significantly induced by Cd and Pb, rather by Cu and Zn. This is the first report on heavy metal-induced changes of CYP3A4 activity in earthworms. Among the four heavy metals, Cd was the most potent inducing EROD and CYP3A4. While EROD and CYP3A4 activities showed a similar trend, EROD is more sensitive than CYP3A4 activity in E. fetida as a biomarker for heavy metals pollution. (C) 2012 Elsevier B.V. All rights reserved.