The agricultural soils in the basin of the Aconcagua River exhibit high concentrations of copper compared with other areas with no mining activity. The objective of this work was to assess the toxicity of such areas on the earthworm Eisenia foetida and its relation to copper concentration using the following molecular biomarkers: glutathione-S-transferase (GST), lipid peroxidation (TBARS) and metallothionein concentrations. These soils were also characterised chemically and physically. The results showed significant differences in the concentration of metallothioneins, TBARS and GST activity. A correlation between pH and copper (total, soluble) with the molecular parameters was observed. Metallothionein and GST are proposed as early warning biomarkers of the toxic effects of chemicals in soils.