A laboratory experiment was conducted to determine the effects of different organic wastes such as wheat straw (WS), tea production waste (TEW), tobacco production waste (TOW), cow manure (CM) and hazelnut husk (HH) on dehydrogenase activity (DHA) in casts of earthworm Lumbricus terrestris and surrounding soil using 5% (dry weight) application rates associated with increasing doses of Zn (0, 50, 100, 250, 500 and 1000 mu g g(-1)). Twenty one days after treatment of Zn and organic wastes, the DHA analyses were carried out on collected casts and soil samples. In general, all organic waste treatments influenced the DHA, the contents of organic C, N and available Zn in earthworm L. terrestris casts and the surrounding soil in comparison with the control. DHA in casts exceeded that in the surrounding soil without Zn additions. After Zn application of 50 mu g Zn g(-1) in all organic waste treatments and the control, the DHA level in casts and surrounding soil increased significantly. It decreased by application rates of 100, 250, 500 and 1000 mu g Zn g(-1) consecutively in all organic waste applications. The addition of wastes with low C/N ratio and high Zn content (TEW, TOW, CM) inhibited the DHA in both cast and surrounding soil. (c) 2007 Elsevier Ltd. All rights reserved.