The effect of heavy metals Cu and Zn on dehydrogenase and protease activity of the substrate during vermicomposting was investigated. Three dosages of Cu and Zn were tested in mesocosm experiments to investigate their bioaccumulation and impact on the reproduction of Eisenia fetida. Cu accumulated within the worm tissues in dosage concentrations up to a maximum level of 213 mg Cu kg(-1). The number of juveniles decreased from the lowest to highest dosages of Cu and Zn after 10 weeks of the experiment. Dehydrogenase showed a strong negative correlation (P < 0.01) with increased dosage of Cu, while protease remained unaffected. An overall reduction on dehydrogenase activity with increasing dosages of Cu and Zn indicated that these metals would impact detrimentally on the soil microbiology and consequently the stabilisation of the dosed media. (c) 2005 Elsevier Ltd. All rights reserved.